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Published on: 28/05/2021
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Questions + Answers key
Take MCQ Maths Test1.
If, A = \(\left[ \begin{matrix} a & 0 \\ 1 & 1 \end{matrix} \right] \)and B = \(\left[ \begin{matrix} 1 & 0 \\ 5 & 1 \end{matrix} \right] \) find all those values of a for which A = B
2.
If \(y={ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n }\)prove that \(\frac { dy }{ dx } =\frac { ny }{ \sqrt { { x }^{ 2 }+{ a }^{ 2 } } } \)
3.
Consider identity function \(I_{ N }+I_{ N }:N\rightarrow N\) defined as:
\(I_{ N }(x)=x\forall x\in N.\)
Show that although \(I_{ N }\) is onto but \(I_{ N }+I_{ N }:N\rightarrow N\)defined as:
\((I_{ N }+I_{ N })(x)+I_{ N }(x)=x+x=2x\) is onto.
4.
An equilateral triangle has each side equal to a. If the co-ordinates of its vertices are (x1,y1), (x2,y2) and (x3, y3), show that \(\left| \begin{matrix} x_1 &y_1 &1 \\x_2 &y_2 &1 \\x_3 &y_3 &1 \end{matrix} \right| ^2={3\over4}a^4\)
5.
The decay rate of radium at any time is proportional to its mass at that time. The mass is \({m}_{0}\) at \(t=0.\) Find the time when the mass will be halved
1.
No values of \(\alpha\) can be found for which A2 = B is true
2.
We have \(y={ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n }\) ....(1)
\(\frac { dy }{ dx } =n{ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n-1 }\frac { d }{ dx } \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} \)
\(=n{ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n-1 } \)
\(\left[ 1+\frac { 1 }{ 2\sqrt { { x }^{ 2 }+{ a }^{ 2 } } } (2x+0) \right] \)
\(=n{ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n-1 }\left\{ \frac { \sqrt { { x }^{ 2 }+{ a }^{ 2 } } +x }{ \sqrt { { x }^{ 2 }+{ a }^{ 2 } } } \right\} \)
\(=\frac { n{ \left\{ x+\sqrt { { x }^{ 2 }+{ a }^{ 2 } } \right\} }^{ n } }{ \sqrt { { x }^{ 2 }+{ a }^{ 2 } } } =\frac { ny }{ \sqrt { { x }^{ 2 }+{ a }^{ 2 } } } \)
which is true.
3.
Here \(I_{ N }\) is onto. [Given]
But \(I_{ N }+I_{ N }\) is not onto
[∵ We can find 3 in the co−domain N, where 3 is not a multiple of 2]
4.
\(A={1\over2}\begin{vmatrix}x_1&y_1&1\\x_2&y_2&1\\x_3&y_3&1 \end{vmatrix}\)
But in equilateral triangle of each side equal toa, area = \(\sqrt{3}a^2\over4\)
= \({\sqrt{3}a^2\over4}={1\over2}\begin{vmatrix}x_1&y_1&1\\x_2&y_2&1\\x_3&y_3&1 \end{vmatrix}\)
\(\Rightarrow\begin{vmatrix}x_1&y_1&1\\x_2&y_2&1\\x_3&y_3&1 \end{vmatrix}={\sqrt{3}a^2\over2}\)
Hence,\(\left| \begin{matrix} x_1 &y_1 &1 \\x_2 &y_2 &1 \\x_3 &y_3 &1 \end{matrix} \right| ^2={3\over4}a^4\) is true.
5.
Let 'M' be the mass at time t.
By the question, \(\frac { dM }{ dt } =-k M\Rightarrow \frac { dM }{ M } -k\quad dt\)
|Variables Separable
Integrating, \(\int { \frac { dM }{ M } } =-k\int { 1.\quad dt+c } \)
\(\Rightarrow\) \(log|M|=-kt+c\) ...(1)
When \(t=0, M={m}_{0}, \ \therefore log|{m}_{0}|=0+c\)
\(\Rightarrow c=log|{m}_{0}|.\)
Putting in (1),\(log|M|=-kt+log|{ m }_{ 0 }|.\)
When \(M=\frac { { m }_{ 0 } }{ 2 } ,log|\frac { { m }_{ 0 } }{ 2 } |=-kt+log|{ m }_{ 0 }|\)
\(\Rightarrow\) \(log|\frac { 1 }{ 2 } |=-kt\Rightarrow log\quad 2=-kt\)
\(\Rightarrow\) \(t=\frac { 1 }{ k } log\quad 2,\)
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