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12th Standard Maths Important 3 Mark Questions

12th Standard

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Maths

Time : 01:30:00 Hrs
Total Marks : 90

    Answer all the following Questions.

    30 x 3 = 90
  1. Find the inverse of the matrix \(\left[ \begin{matrix} 2 & -1 & 3 \\ -5 & 3 & 1 \\ -3 & 2 & 3 \end{matrix} \right] \).

  2. Find the inverse (if it exists) of the following:
    \(\left[ \begin{matrix} 5 & 1 & 1 \\ 1 & 5 & 1 \\ 1 & 1 & 5 \end{matrix} \right] \)

  3. Find the rectangular form of the complex numbers
    \(\left( cos\frac { \pi }{ 6 } +isin\frac { \pi }{ 6 } \right) \left( cos\frac { \pi }{ 12 } +isin\frac { \pi }{ 12 } \right) \)

  4. If \(2cos\ \alpha=x+\frac { 1 }{ x } \) and \(2cos\ \beta =y+\frac { 1 }{ y } \), show that ​\(\frac { { x }^{ m } }{ { y }^{ n } } -\frac { { y }^{ n } }{ { x }^{ m } } =2isin\left( m\alpha -n\beta \right) \)

  5. Solve the equation
    2x- 9x+ 10x = 3

  6. Let p and q be rational numbers such that \(\sqrt{q}\) is irrational. If p + \(\sqrt{q}\) is a root of a quadratic equation with rational coefficients, then p − \(\sqrt{q}\) is also a root of the same equation.

  7. Find the value of
    \(cos\left( { sin }^{ -1 }\left( \frac { 4 }{ 5 } \right) -{ tan }^{ -1 }\left( \frac { 3 }{ 4 } \right) \right) \)

  8. The position of a point P(x1 , y 1)  with respect to a given circle x2 + y2 + 2gx + 2 fy + c = 0 in the plane containing the circle is outside or on or inside the circle according as
    \(x_{1}^{2}+y_{1}^{2}+2 g x_{1}+2 f y_{1}+c \text { is } \begin{cases}>0 & \text { or } \\ =0 & \text { or } \\ <0 & \end{cases}\)

  9. Find the acute angle between the planes \(\vec { r } .(2\hat { i } +2\hat { j } +2\hat { k } )\) and 4x-2y+2z = 15.

  10. The acute angle \(\theta\) between the two planes \(\vec{r} \cdot \vec{n}_{1}=p_{1} \text { and } \vec{r} \cdot \vec{n}_{2}=p_{2}\) is given by \(\theta=\cos ^{-1}\left(\frac{\left|\vec{n}_{1} \cdot \vec{n}_{2}\right|}{\left|\vec{n}_{1}\right|\left|\vec{n}_{2}\right|}\right)\)

  11. Using the Rolle’s theorem, determine the values of x at which the tangent is parallel to the x -axis for the following functions:
    \(f(x)=\sqrt{x}-\frac{x}{3}, x\in [0,9]\)

  12. Evaluate the following limit, if necessary use l ’Hôpital Rule
    \(​​​​​​\underset { x\rightarrow \infty }{ lim } \ { \left( 1+\frac { 1 }{ x } \right) }^{ x }\)

  13. If A is non-singular, then 
    \((i)\ \left|A^{-1}\right|=\frac{1}{|A|} \)
    \((ii)\ \left(A^{T}\right)^{-1}=\left(A^{-1}\right)^{T} \)
    \((iii)\ (\lambda A)^{-1}=\frac{1}{\lambda} A^{-1},\)
    where is \(\lambda\) non-zero scalar

  14. Let \(f(x)=\sqrt [ 3 ]{ x } \). Find the linear approximation at x = 27. Use the linear approximation to approximate \(\sqrt [ 3 ]{ 27.2 } \)

  15. If α and β are the roots of the quadratic equation 17x2+43x−73 = 0 , construct a quadratic equation whose roots are α + 2 and β + 2.

  16. Show that \(\int ^\frac{2\pi}{0}_{0}\) g(cos x)dx = 2 \(\int ^{\pi}_{0}\) g(cosx)dx where g(cos x) is a function of cos x

  17. Evaluate the following:
    \(\int _{ 0 }^{ \frac { 1 }{ 2 } }{ \frac { { e }^{ { a\ sin }^{ -1x } }{ sin }^{ -1 }x }{ \sqrt { 1-{ x }^{ 2 } } } dx } \)

  18. Find the differential equation of the family of circles passing through the points (a, 0) and (−a, 0).

  19. Two balls are chosen randomly from an urn containing 6 white and 4 black balls. Suppose that we win Rs. 30 for each black ball selected and we lose Rs. 20 for each white ball selected. If X denotes the winning amount, then find the values of X and number of points in its inverse images.

  20. Write each of the following sentences in symbolic form using statement variables p and q.
    (i) 19 is not a prime number and all the angles of a triangle are equal.
    (ii) 19 is a prime number or all the angles of a triangle are not equal
    (iii) 19 is a prime number and all the angles of a triangle are equal
    (iv) 19 is not a prime number

  21. Solve: 3x+ay = 4, 2x + ay = 2, a ≠ 0 by Cramer's rule.

  22. Evaluate \(\int _{ 0 }^{ \frac { \pi }{ 2 } }{ { cos }^{ 10 }xdx } \)

  23. By using the properties of definite integrals, I evaluate \(\int_{0}^{1}|x-1| d x\)

  24. Solve:\(\frac { dy }{ dx } =\frac { 1-cosx }{ 1+cosx } \)

  25. In a continuous distribution the p.d.f of x is \(f(x)=\left\{\begin{array}{c} \frac{3}{4} x(2-x), 0, Find the mean and variance of the distribution.

  26. The p.d.f. of X is given by 

    x -2 2 5
    P(X-x) \( \frac{1}{4} \) \( \frac{1}{4} \) \( \frac{1}{2}\)

    then find 4E(X²) - var(2X)

  27. The probability that an event A happens in one treat of an experiment is 0.4. Three independent treats of the experiment are performed. Find the probability that the event A happens atleast once?

  28. Show that f(x, y) = \(\frac { { x }^{ 2 }-{ y }^{ 2 } }{ { y }^{ 2 }+1 } \) is continuous at every (x, y) ∈ R2

  29. Let U(x, y, z) = x2 − xy + 3 sin z, x, y, z ∈ R Find the linear approximation for U at (2,−1,0).

  30. Find ∆f and df for the function f for the indicated values of x, ∆x and compare
    (1) f(x) = x3 - 2x2 ; x = 2, ∆ x = dx = 0.5
    (2) f(x) = x2 + 2x + 3; x = -0.5, ∆x = dx = 0.1 

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