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Published on: 22/05/2021
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Questions + Answers key
Take MCQ Maths Test1.
Sketch the region \(\left\{(x, y): y=\sqrt{4-x^{2}}\right\}\) and X-axis. Find the area of the region using integration.
2.
Evaluate \(\int \tan ^{2} x \sec ^{4} x d x\)
3.
Evaluate the integral \(\int { \frac { \sin ^{ -1 }{ x } }{ { \left( 1-{ x }^{ 2 } \right) }^{ 3/2 } } } dx.\)
4.
Evaluate the integral \(\int { \frac { \sqrt { 1+{ x }^{ 2 } } }{ { x }^{ 4 } } } dx.\)
5.
Evaluate:\(\int { \frac { { x }^{ 3 }+x }{ { x }^{ 4 }-9 } } dx.\)
6.
Evaluate :\(\int { \tan ^{ 8 }{ x } } \sec ^{ 4 }{ x } dx.\)
7.
Evaluate : \(\int { \frac { dx }{ \sqrt { (x-a)(\beta -x) } } } ,\beta >a.\)
8.
Verify the following, using the concept of integration as an antiderivative: \(\int { \frac { { x }^{ 3 } }{ x+1 } } dx=x-\frac { 1 }{ 2 } { x }^{ 2 }+\frac { 1 }{ 3 } { x }^{ 3 }-\log { \left| x+1 \right| } +C.\)
9.
Determine the minimum value of Z = 3x + 2y (if any), if the feasible region for an LLP is shown in the figure:

10.
Show that the vector \(\overset { \rightarrow }{ a } \), \(\overset { \rightarrow }{ b } \) and \(\overset { \rightarrow }{ c } \) are coplanar if \(\overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ,\overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } \ and \ \overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \) are coplanar.
11.
Prove that:\(\left[ \overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ,\overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } ,\overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } ]=2[\overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] \)
12.
Lagrange's identify prove that : \({( }{ \overrightarrow { a } *\overrightarrow { b) } }^{ 2 }=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } -{ ( }{ \overrightarrow { a } .\overrightarrow { b) } }^{ 2 }\)
13.
If \(\overrightarrow { r } =x\hat { i } +y\hat { j } +z\hat { k } \) ,then find \((\vec{r} \times \hat{i}) \cdot(\vec{r} \times \hat{j})+x y\)
14.
If A and B are two points vectors and respectively. write the position vectors of a point of a P, which divides the line segment AB internally in the ratio 1 : 2
15.
Find the value of 'p' for which the vectors:\(3\overset { \wedge }{ i } -2\overset { \wedge }{ j } +9\overset { \wedge }{ k } \) and \(\overset { \wedge }{ i } -2p\overset { \wedge }{ j } +3\overset { \wedge }{ k } \) are paralell.
16.
Using vector, find the value of 'k' such that the point: (k, -10, 3), (1, -1, 3) and (3, 5, 3) are collinear.
17.
Find all vectors of magnitude 10\(\sqrt { 3 }\) that are perpendicular to the plane of:
\(\overset { \wedge }{ i } +2\overset { \wedge }{ j } +\overset { \wedge }{ k } \ and\ -\overset { \wedge }{ i } +3\overset { \wedge }{ j } +4\overset { \wedge }{ k } \)
18.
Find the equation of a curve passing through the origin, given that the slope of the tangent to the curve at any point (x, y) is the equal to the sum of the co-ordinates of the point.
19.
Show that for \(a\ge 1\) \(f(x)=\sqrt { 3 } sinx-cosx-2ax+4\) is increasing in R.
20.
Find the area of the region bounded by the curves:
x = at2 and y = 2at between the ordinates corresponding to t = 1 and t = 2.
21.
Find the area of the region bounded by the parabola y2 = 2x and the straight line x - y = 4.
22.
Is the binary operation '*' defined on Z (set of integers) by:
\(m*n=m-n+mn\quad for\quad all\quad m,n\in Z\) commutative?
23.
If the mappings f and g are given by:
f = {(1, 2), (3, 5) (4, 1) and g = {(2, 3), (5, 1), (1, 3)}, write fog.
24.
If \(\Delta =\left| \begin{matrix} 1 & x & x^{ 2 } \\ 1 & y & { y }^{ 2 } \\ 1 & z & { z }^{ 2 } \end{matrix} \right| ,{ \Delta }_{ 1 }=\left| \begin{matrix} 1 & 1 & 1 \\ yz & zx & xy \\ x & y & z \end{matrix} \right| \)then prove that \(\Delta+\Delta_1=0\)
1.
Given region is \(\left\{(x, y): y=\sqrt{4-x^{2}}\right\} \text { and } X \text { -axis. }\)
We have,\(y=\sqrt{4-x^{2}}\)
We have,\(y=\sqrt{4-x^{2}}\)
\(\Rightarrow y^{2}=4-x^{2} \Rightarrow x^{2}+y^{2}=4\)
This represent the equation of circle having centre (0, 0) and radius 2.
But original equation is \(y=\sqrt{4-x^{2}}\). So y is positive. It means that, we have to take a curve above the X-axis.
Thus, only semi-circle is formed above the X-axis
Since, the region is symmetrical about Y-axis
\(\therefore\) Area of shaded region,
\(A=2 \int_{0}^{2} y d x=2 \int_{0}^{2} \sqrt{4-x^{2}} d x=2 \int_{0}^{2} \sqrt{2^{2}-x^{2}} d x\)
\(=2\left[\frac{x}{2} \sqrt{2^{2}-x^{2}}+\frac{2^{2}}{2} \cdot \sin ^{-1} \frac{x}{2}\right]_{0}^{2} \)
\(=2\left[\frac{2}{2} \cdot 0+2 \cdot \frac{\pi}{2}-\frac{0}{2} \cdot 2-2 \sin ^{-1}(0)\right] \)
\(=2\left[2 \cdot \frac{\pi}{2}+0\right]=2 \pi \text { sq units } \)
2.
Let \(I=\int \tan ^{2} x \sec ^{4} x d x=\int \tan ^{2} x \sec ^{2} x \sec ^{2} x d x\)
\(=\int \tan ^{2} x\left(1+\tan ^{2} x\right) \sec ^{2} x d x \quad\left[\because \sec ^{2} x=1+\tan ^{2} x\right]\)
Now, put \(\tan x=t \Rightarrow \sec ^{2} x d x=d t\)
\( \therefore I =\int\left(t^{2}-1\right) \cdot t^{2} d t=\int\left(t^{4}-t^{2}\right) d t=\frac{t^{3}}{5}-\frac{t^{3}}{3}+C\)
\( =\frac{1}{5} \sec ^{5} x-\frac{1}{3} \sec ^{3} x+C \quad[\because t=\sec x] \)
3.
\(Put\ \sin ^{ -1 }{ x } =t\) i.e.x = sin t
so that \(\frac { 1 }{ \sqrt { 1-{ x }^{ 2 } } } dx=dt.\)
\(\therefore I=\int { \frac { t }{ (1-\sin ^{ 2 }{ t) } } } dt=\int { \frac { t }{ \cos ^{ 2 }{ t } } } dt\)
\(=\int { t\sec ^{ 2 }{ t } dt } \)
\(=t\tan { t } -\int { (1) } \tan { t } dt\)
[Integration by Parts]
\(=t\tan { t } +\log { \left| \cos { t } \right| } +c\)
\(=\sin ^{ -1 }{ x } .\frac { x }{ \sqrt { 1-{ x }^{ 2 } } } +\log { \left| \sqrt { 1-{ x }^{ 2 } } \right| } +c\)
4.
\(I=\int { \sqrt { \left( \frac { 1 }{ { x }^{ 2 } } +1 \right) } } \frac { 1 }{ { x }^{ 3 } } dx.\)
\(Put\ \frac { 1 }{ { x }^{ 2 } } +1=t\)so that \(-\frac { 2 }{ { x }^{ 3 } } dx=dt\quad i.e.\frac { dx }{ { x }^{ 3 } } =-\frac { dt }{ 2 } .\)
\(\therefore I=\int { \sqrt { t } } \left( -\frac { dt }{ 2 } \right) =-\frac { 1 }{ 2 } \int { { t }^{ 3/2 } } dt\)
\(=-\frac { 1 }{ 2 } .\frac { { t }^{ 3/2 } }{ 3/2 } +c=-\frac { 1 }{ 3 } { \left( 1+\frac { 1 }{ { x }^{ 2 } } \right) }^{ 3/2 }+c.\)
5.
\(I= \int { \frac { { x }^{ 3 }+x }{ { x }^{ 4 }-9 } } dx.\)
\(=\frac { { x }^{ 3 } }{ { x }^{ 4 }-9 } dx+\int { \frac { xdx }{ { x }^{ 4 }-9 } } ..(1)\)
Now, \({ I }_{ 1 }=\frac { { x }^{ 3 } }{ { x }^{ 4 }-9 } dx.\)
\(Put\ { x }^{ 4 }=t\)so that \(4{ x }^{ 3 }dx=dt\ i.e. { x }^{ 3 }dx=\frac { 1 }{ 4 } dt.\)
\(\therefore { I }_{ 1 }=\int { \frac { \frac { 1 }{ 4 } dt }{ t-9 } } =\frac { 1 }{ 4 } \int { \frac { dt }{ t-9 } } \)
\(=\frac { 1 }{ 4 } \log { \left| t-9 \right| } +{ c }_{ 1 }=\frac { 1 }{ 4 } \log { \left| { x }^{ 4 }-9 \right| } +{ c }_{ 1 }.\)
And \({ I }_{ 2 }=\int { \frac { x }{ { x }^{ 4 }-9 } } dx.\)
\(Put\ { x }^{ 2 }=u\)so that \(2xdx=du\ i.e. xdx=\frac { 1 }{ 2 } du.\)
\(\therefore { I }_{ 2 }=\int { \frac { \frac { 1 }{ 2 } du }{ { u }^{ 2 }-9 } } =\frac { 1 }{ 2 } \int { \frac { du }{ { u }^{ 2 }-3^{ 2 } } } \)
\(=\frac { 1 }{ 2 } .\frac { 1 }{ 2(3) } \log { \left| \frac { u-3 }{ u+3 } \right| } +{ c }_{ 2 }= \frac { 1 }{ 12 } \log { \left| \frac { { x }^{ 2 }-3 }{ { x }^{ 2 }+3 } \right| } +{ c }_{ 2 }.\)
\(\therefore \ From(1), I=\ \frac { 1 }{ 4 } \log { \left| { x }^{ 2 }-9 \right| } +\frac { 1 }{ 12 } \log { \left| \frac { { x }^{ 2 }-3 }{ { x }^{ 2 }+3 } \right| } +{ c }.\)
Where \({ c }_{ 1 }+{ c }_{ 2 }=c\)
6.
\(I=\int { \tan ^{ 8 }{ x } } (\sec ^{ 2 }{ x } )\)
\(=\int { \tan ^{ 8 }{ x } } (\sec ^{ 2 }{ x } )\sec ^{ 2 }{ x } dx\)
\(=\int { \tan ^{ 8 }{ x } } (1+\tan ^{ 2 }{ x } )\sec ^{ 2 }{ x } dx\)
\(=\int { \tan ^{ 8 }{ x } } \sec ^{ 4 }{ x } dx+ \int { \tan ^{ 10 }{ x } \sec ^{ 2 }{ x } } dx.\)
\(Put\ \tan { x } =t\) so that \(\sec ^{ 2 }{ x } dx=dt\)
\(\therefore I= \int { { t }^{ 8 } } dt+\int { { t }^{ 10 } } dt=\frac { { t }^{ 9 } }{ 9 } +\frac { { t }^{ 11 } }{ 11 } +c\)
\(I= \frac { \tan ^{ 11 }{ x } }{ 11 } +\frac { \tan ^{ 9 }{ x } }{ 9 } +C.\)
7.
Let \(I=\int { \frac { dx }{ \sqrt { (x-a)(\beta -x) } } } \)
\(Put\ x-a={ t }^{ 2 }\) so that \(dx=2t\ dt\)
Also \(\beta -x=\beta -({ t }^{ 2 }+(\beta -a)=(\beta -a)-{ t }^{ 2 }\)
\(\therefore I= \int { \frac { 2t\quad dt }{ { t }^{ 2 }({ \beta -a-t }^{ 2 }) } } =\int { \frac { 2\quad dt }{ ({ \beta -a)-t }^{ 2 } } } \)
\(=2\int { \frac { dt }{ \sqrt { { (\sqrt { \beta -a } ) }^{ 2 }-{ t }^{ 2 } } } } =2\sin ^{ -1 }{ \frac { t }{ \sqrt { \beta -a } } } +c\)
\(=2\sin ^{ -1 }{ \sqrt { \frac { x-a }{ \beta -a } } } +C\)
8.
\( \frac { d }{ dx } \left( x-\frac { { x }^{ 2 } }{ 2 } +\frac { { x }^{ 3 } }{ 3 } -\log { \left| x+1 \right| } +C \right) \)
\(=1-\frac { 1 }{ 2 } (2x)+\frac { 1 }{ 3 } (3{ x }^{ 2 })-\frac { 1 }{ x+1 } +0\)
\(=1-x+{ x }^{ 2 }-\frac { 1 }{ 1+x } =\frac { 1-x+{ x }^{ 2 }(1+x)-1 }{ 1+x } \)
\(=\frac { 1+{ x }^{ 3 }-1 }{ 1+x } =\frac { { x }^{ 3 } }{ x+1 } .\)
\(\left( x-\frac { 1 }{ 2 } { x }^{ 2 }+\frac { 1 }{ 3 } { x }^{ 3 }-\log { \left| x+1 \right| } +C \right) \)
\(=\int { \frac { { x }^{ 3 } }{ x+1 } } dx.\)
9.
The feasible region is unbounded.
∴ Minimum value of Z may or may not exist.
Applying Corner Point Method, we have:
| Corner Point | Value of Z |
| A : (12,0) | 36 |
| B : (4,2) | 16 |
| C : (1,5) | 13 (Minimum) |
| D : (0,10) | 20 |
We graph 3x + 2y < 13.
It is observed that the open half plane determined by 3x + 2y < 13 and R do not have a common point.
Hence, Minimum value of Z = 13.
10.
Since \(\overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ,\overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } \ and\ \overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \) are complannar.
\(\therefore\) \(\overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ).\left[ (\overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } )\times (\overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } ) \right] =0\)
\(\Rightarrow (\overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ).\left[ \overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } \times \overset { \rightarrow }{ b } \times \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ c } \times \overset { \rightarrow }{ c } +\overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \right] =0\)
\(\Rightarrow (\overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ).(\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } +\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ a } +\overset { \rightarrow }{ c } \times \overset { \rightarrow }{ a } )=0 \left[ \because \overset { \rightarrow }{ c } \times \overset { \rightarrow }{ c } =\overset { \rightarrow }{ 0 } \right] \)
\(\Rightarrow \overset { \rightarrow }{ a } .(\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } )+\overset { \rightarrow }{ a } .(\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ a } )+\overset { \rightarrow }{ a } .(\overset { \rightarrow }{ c } \times \overset { \rightarrow }{ a } )+\overset { \rightarrow }{ b } .(\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } )+\overset { \rightarrow }{ b } .(\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ a } )+\overset { \rightarrow }{ b } .(\overset { \rightarrow }{ c } \times \overset { \rightarrow }{ a } )=0\)
\(\Rightarrow 2\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] =0\)
\(\Rightarrow 2\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] =0\Rightarrow \left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] =0\)
\(\Rightarrow \) \(\overset { \rightarrow }{ a } ,\overset { \rightarrow }{ b } \ and\ \overset { \rightarrow }{ c } \) are coplanar.
11.
LHS\(=\left[ \overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } ,\overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } ,\overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \right] \)
\(=\left[ \left( \overset { \rightarrow }{ a } +\overset { \rightarrow }{ b } \right) *\left( \overset { \rightarrow }{ b } +\overset { \rightarrow }{ c } \right) \right] .\left( \overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \right) \)
\(=\left[ \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ b } +\overset { \rightarrow }{ a } \times \overset { \rightarrow }{ c } +\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ b } \right] .\left( \overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \right) \)
\(=\left[ \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ b } +\overset { \rightarrow }{ a } \times \overset { \rightarrow }{ c } +\overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } \right] .\left( \overset { \rightarrow }{ c } +\overset { \rightarrow }{ a } \right) \)
\(=\left( \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ b } \right) .\overset { \rightarrow }{ c } +\left( \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ b } \right) .\overset { \rightarrow }{ a } +\left( \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ c } \right) .\overset { \rightarrow }{ c } +\left( \overset { \rightarrow }{ a } \times \overset { \rightarrow }{ c } \right) .\overset { \rightarrow }{ a } +\left( \overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } \right) .\overset { \rightarrow }{ c } +\left( \overset { \rightarrow }{ b } \times \overset { \rightarrow }{ c } \right) .\overset { \rightarrow }{ a } \\ \)
\(=\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] +\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ a } \right] +\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ c } \overset { \rightarrow }{ c } \right] +\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ c } \overset { \rightarrow }{ a } \right] +\left[ \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \overset { \rightarrow }{ c } \right] +\left[ \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \overset { \rightarrow }{ a } \right] \)
\(=\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\overset { \rightarrow }{ 0 } +\left[ \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \overset { \rightarrow }{ a } \right] \)
\(=\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] +\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] =2\left[ \overset { \rightarrow }{ a } \overset { \rightarrow }{ b } \overset { \rightarrow }{ c } \right] =RHS\\ \)
12.
\({ ( }{ \overrightarrow { a } *\overrightarrow { b) } }^{ 2 }={ \overset { \rightarrow }{ { (|a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } sin\theta { \overrightarrow { n } ) }^{ 2 } }\)
\(=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } sin\theta { \overrightarrow { n } }^{ 2 }=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } sin\theta { \overrightarrow { n } }^{ 2 }\) \([\because { \overrightarrow { n } }^{ 2 }=\overrightarrow { n } .\overrightarrow { n } =(1)cos0°=1]\)
\(=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } (1-{ cos }^{ 2 }°\theta )\)
\(=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } -\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |b| }^{ 2 } } { cos }^{ 2 }°\theta \)
\(=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |{ b }| }^{ 2 } } -{ (\overrightarrow { a } .\overrightarrow { b } ) }^{ 2 }{ cos }^{ 2 }°\theta \)
\(=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |{ b }^{ 2 }| }^{ 2 } } -{ (\overrightarrow { a } .\overrightarrow { b } ) }^{ 2 }\)
Other (I) \({ (\overrightarrow { a } .\overrightarrow { b } ) }^{ 2 }=\overset { \rightarrow }{ { |a| }^{ 2 } } \overset { \rightarrow }{ { |{ b }| }^{ 2 } } -{ (\overrightarrow { a } *\overrightarrow { b } ) }^{ 2 }\)
(II) \({ (\overrightarrow { a } *\overrightarrow { b } ) }^{ 2 }+{ (\overrightarrow { a } .\overrightarrow { b } ) }^{ 2 }=\overset { \rightarrow }{ { |a| } } \overset { \rightarrow }{ { |{ b }| }^{ 2 } } \)
13.
Here \(\overrightarrow { r } *\hat { i } \) \(=(x\hat { i } +y\hat { j } +z\hat { k } )*\hat { i } \)
\(=x(i*\hat { j } )+y(\hat { j } *i)+z(\hat { k } *i)\)
\(=x\overrightarrow { (0) } +y(-\hat { k } )+z(\hat { j } )\)
\(=-y\hat { k } +z\hat { j } \) ...(1)
and \(\overrightarrow { r } *\hat { j } =(x\hat { i } +y\hat { j } +z\hat { k } )*\hat { i } \)
\(=x(i*\hat { j } )+y(\hat { j } *\hat { j } )+z(\hat { k } *\hat { j } )\)
\(=x(\hat { k } )+y\overrightarrow { (0) } +z(-\hat { i } )\)
\(=-y\hat { k } -z\hat { i } \) ...(2)
\(\therefore (\overrightarrow { r } *\hat { i } ).(\overrightarrow { r } *\hat { j } )+xy\)
\(=(-y\hat { k } +z\hat { j } ).(x\hat { k } +z\hat { j } )+xy\)
\(=-yx(\hat { k } .\hat { k } )+yz(\hat { k } .\hat { i } )+zx(\hat { j } .\hat { k } )-{ z }^{ 2 }(\hat { j } .\hat { i } )+xy\)
\(=-yx(1)+yz(0)+zx(0)-{ z }^{ 2 }(0)+xy\)
\(=-xy+xy=0\)
14.
The position vector of P
\(=\frac { 1.(6\overset { \rightarrow }{ b } -\overset { \rightarrow }{ a } )+(2\overset { \rightarrow }{ a } -\overset { \rightarrow }{ b } ) }{ 1+2 } \)
\(=\frac { 6\overset { \rightarrow }{ b } -\overset { \rightarrow }{ a } +4\overset { \rightarrow }{ a } -\overset { \rightarrow }{ b } }{ 3 } =\frac { 3\overset { \rightarrow }{ a } }{ 3 } =\overset { \rightarrow }{ a } \)
15.
The given vectors \(3\overset { \wedge }{ i } -2\overset { \wedge }{ j } +9\overset { \wedge }{ k } \) and \(\overset { \wedge }{ i } -2p\overset { \wedge }{ j } +3\overset { \wedge }{ k } \) are parallel
if \(\frac { 3 }{ 1 } =\frac { 2 }{ -2p } =\frac { 9 }{ 3 } 3=\frac { 1 }{ -p } =3\)
if \(p=-\frac { 1 }{ 3 } \)
16.
Let \(\overset { \rightarrow }{ a } =k\overset { \wedge }{ i } -10\overset { \wedge }{ j } +3\overset { \wedge }{ k } ,\) and \(\overset { \rightarrow }{ b } =\overset { \wedge }{ i } -\overset { \wedge }{ j } +3\overset { \wedge }{ k } \) and \(\overset { \rightarrow }{ c } =3\overset { \wedge }{ i } +5\overset { \wedge }{ j } +3\overset { \wedge }{ k } \)
the given points are colinear if \(\left| \begin{matrix} k & -10 & 3 \\ 1 & -1 & 3 \\ 3 & 5 & 3 \end{matrix} \right| \)
If k(-3-15) +10(3-9) + 3(5+3) = 0
If -8k - 60 + 24 = 0
If 18k = -36
If k = -2
17.
Let \(\overset { \rightarrow }{ a } =\overset { \wedge }{ i } +2\overset { \wedge }{ j } +\overset { \wedge }{ k } \ and\ \overset { \rightarrow }{ b } =-\overset { \wedge }{ i } +3\overset { \wedge }{ j } +4\overset { \wedge }{ k } \)
Then \(\overset { \rightarrow }{ a } *\overset { \rightarrow }{ b } =\left| \begin{matrix} \overset { \wedge }{ i } & \overset { \wedge }{ j } & \overset { \wedge }{ k } \\ 1 & 2 & 1 \\ -1 & 3 & 4 \end{matrix} \right| \)
\(\therefore |\overset { \rightarrow }{ a } *\overset { \rightarrow }{ b } |=\sqrt { { (5) }^{ 2 }+{ (-5) }^{ 2 }+{ (5) }^{ 2 } } =\sqrt { { 3(5) }^{ 2 } } \)
\(\pm 10\sqrt { 3 } \left( \frac { 5\overset { \wedge }{ i } -5\overset { \wedge }{ j } +5\overset { \wedge }{ k } }{ 5\sqrt { 3 } } \right) i.e\pm 10(\overset { \wedge }{ i } -\overset { \wedge }{ j } +\overset { \wedge }{ k } )\)
\(\therefore\) The unit vector perpendicular to the plane \(\overset { \rightarrow }{ a } \) and \(\overset { \rightarrow }{ b } \) is given by:
Hence, the vector of magnitude 10\(\sqrt { 3 }\) that are perpendicular to the plane of \(\overset { \rightarrow }{ a } \) and \(\overset { \rightarrow }{ b } \) are
18.
We know that the slope of the tangent to the curve is \(\frac { dy }{ dx } .\)
By the question, \(\frac { dy }{ dx } =x+y\)
\(\Rightarrow\) \(\frac { dy }{ dx } -y=x\) .(1)
Here \('P'=-1\) and \('Q'=x.\)
\(\therefore\) I.F. \(={ e }^{ \int { Pdx } }={ e }^{ \int { -1.dx } }={ e }^{ -x }\)
Multiplying (1) by \({ e }^{ -x },\) we get:
\({ e }^{ -x }.\frac { dy }{ dx } -y.{ e }^{ -x }=x.{ e }^{ -x }.\)
\(\Rightarrow\) \(\frac { d }{ dx } \left( y.{ e }^{ -x } \right) =x{ e }^{ -x }.\)
Integrating,
\(y.{ e }^{ -x }=\int { x.{ e }^{ -x } } dx+C\)
\(=x.\frac { { e }^{ -x } }{ -1 } -\int { \left( 1 \right) } \frac { { e }^{ -x } }{ -1 } dx+C\)
[Integrating by Parts]
\(=-x{ e }^{ -x }+\int { { e }^{ -x } } dx+C\)
\(=-x{ e }^{ -x }+\frac { { e }^{ -x } }{ -1 } +C\)
\(\Rightarrow\) \(y=-x-1+C\quad { e }^{ x }\)
Since the curve passes through of the origin(0,0),
\(\therefore\) \(0=-0-1+C\quad { e }^{ 0 }\Rightarrow C=1.\)
Putting in (2),\(y=-x-1+{ e }^{ x }\)
\(\Rightarrow x+y+1={ e }^{ x },\)
Which is the requested equation of the curve.
19.
We have:
\(f(x)=\sqrt { 3 } sinx-cosx-2ax+b\)
\(\therefore f(x)=\sqrt { 3 } cosx-sinx-2a\)
\(=2\left( \frac { \sqrt { 3 } }{ 2 } cosx+\frac { 1 }{ 2 } sinx \right) -2a\)
\(=2cos\left( x-\frac { \pi }{ 6 } \right) -2a=2\left\lfloor cos\left( x-\frac { \pi }{ 6 } \right) -a \right\rfloor \)
\(= \ge 0.\)
20.
We have : x = at2 ..(1)
and y = 2at ...(2)
From (2) \(t=\frac { y }{ 2a } \)
Putting in (1), \(x=a\left( \frac { { y }^{ 2 } }{ { 4a }^{ 2 } } \right) \Rightarrow { y }^{ 2 }=4ax\)
When t = 1, then from (1), x = a.
When t = 2, then from (2), x = 4a
Therefore, Reqd. area = 2 (area ABCD)
\(=2\overset { 4a }{ \underset { a }{ \int { } } } ydx=2\overset { 4a }{ \underset { a }{ \int { } } } 2\sqrt { ax } dx\)
\(=4\sqrt { a } \left[ \frac { { x }^{ 3/2 } }{ 3/2 } \right] _{ a }^{ 4a }\)
\(=\frac { 8 }{ 3 } \sqrt { a } \left[ { (4a) }^{ 3/2 }-{ (a) }^{ 3/2 } \right] \)
\(=\frac { 8 }{ 3 } { a }^{ 2 }\left[ 8-1 \right] =\frac { 56 }{ 3 } { a }^{ 2 }sq.units\)
21.
The given parabola is y2 = 2x and the given st. line is x - y = 4
Solving (1) and (2):
From (2), x = 4 + y
Putting in (1), y2 = 8 + 2y \(\Rightarrow\) y2 - 2y - 8 = 0 \(\Rightarrow\) (y - 4) (y + 2) = 0 \(\Rightarrow\) y = 4, - 2
When y = 4, then from (3), x = 4 + 4 = 8
When y = -2, then from (3), x = 4 - 2 = 2
Thus the line (2) cuts parabola (2) in the points A (2, -2) and B(8, 4).

The region is shown as shaded in the above figure.
Therefore, Reqd.area
\(=\overset { 4 }{ \underset { -2 }{ \int { } } } \left( 4+y\frac { { y }^{ 2 } }{ 2 } \right) dy=\left[ 4y+\frac { { y }^{ 2 } }{ 2 } -\frac { { y }^{ 3 } }{ 6 } \right] _{ -2 }^{ 4 }\)
\(=\left( 4(4)+\frac { 16 }{ 2 } -\frac { 64 }{ 6 } \right) -\left( -8+\frac { 4 }{ 2 } +\frac { 8 }{ 6 } \right) \)
\(=\left( 16+8\frac { 64 }{ 6 } \right) -\left( -8+2+\frac { 8 }{ 6 } \right) \)
\(=\left( 24-\frac { 64 }{ 6 } \right) +\left( 6-\frac { 8 }{ 6 } \right) =30-\frac { 72 }{ 6 } =30-12=18sq.units\)
22.
No.
For \(1,2\in Z,\quad 1*2=1-2+1.2=1\)
while \(2*1=2-1+2.1=3\)
Hence \(1*2\neq 2*1\)
23.
\((fog)=f(g(x))\)
= {(2, 5), (5, 2), (1, 5)}.
\([\therefore Under\ g:2\rightarrow 3\Rightarrow (2,5);\ etc.\ Under\ f:3\rightarrow 2]\)
24.
\(\Delta_1=\begin{vmatrix} 1&1&1\\yz&zx&xy\\x&y&z\end{vmatrix}\)
\(=\begin{vmatrix}1&yz&x&\\1&zx&y\\1&xy&z \end{vmatrix}\) [Inter-changing rows and columns]
\(={1\over xyz}\begin{vmatrix} x&xyz&x^2\\y&xyz&y^2\\z&xyz&z^2\end{vmatrix}\)[Multiplying R1 by x, R2 by y and R3 by z and taking \(1\over xyz\) outside]
\(={xyz\over xyz}\begin{vmatrix} x&1&x^2\\y&1&y^2\\z&1&z^2\end{vmatrix}\)[Taking xyz common from C2]\
\(=(-1)\begin{vmatrix}1 &x&x^2\\1&y&y^2\\1&z&z^2 \end{vmatrix}\)[Operating C1↔C2]
\(=-\Delta\)
Hence, \(\Delta+\Delta_1\)
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