1.
If \[g\left( x \right) = \left| {\begin{array}{*{20}{c}}
{{a^{ - x}}}&{{e^{x{{\log }_e}a}}}&{{x^2}}\\
{{a^{ - 3x}}}&{{e^{3x{{\log }_e}a}}}&{{x^4}}\\
{{a^{ - 5x}}}&{{e^{5x{{\log }_e}a}}}&1
\end{array}} \right|,\] then
A.
$$g\left( x \right) + g\left( { - x} \right) = 0$$
B.
$$g\left( x \right) - g\left( { - x} \right) = 0$$
C.
$$g\left( x \right) \times g\left( { - x} \right) = 0$$
D.
None of these
Answer :
$$g\left( x \right) + g\left( { - x} \right) = 0$$
View Solution
Discuss Question
\[\begin{array}{l}
g\left( x \right) = \left| {\begin{array}{*{20}{c}}
{{a^{ - x}}}&{{e^{x{{\log }_e}a}}}&{{x^2}}\\
{{a^{ - 3x}}}&{{e^{3x{{\log }_e}a}}}&{{x^4}}\\
{{a^{ - 5x}}}&{{e^{5x{{\log }_e}a}}}&1
\end{array}} \right|\\
= \left| {\begin{array}{*{20}{c}}
{{a^{ - x}}}&{{e^x}}&{{x^2}}\\
{{a^{ - 3x}}}&{{e^{3x}}}&{{x^4}}\\
{{a^{ - 5x}}}&{{e^{5x}}}&1
\end{array}} \right|\left( {{e^{\log {a^x}}} = {a^x}} \right)\\
\Rightarrow g\left( { - x} \right) = \left| {\begin{array}{*{20}{c}}
{{a^x}}&{{a^{ - x}}}&{{x^2}}\\
{{a^{3x}}}&{{a^{ - 3x}}}&{{x^4}}\\
{{a^{5x}}}&{{a^{ - 5x}}}&1
\end{array}} \right|\\
= - \left| {\begin{array}{*{20}{c}}
{{a^{ - x}}}&{{a^x}}&{{x^4}}\\
{{a^{ - 3x}}}&{{a^{3x}}}&{{x^4}}\\
{{a^{ - 5x}}}&{{a^{5x}}}&1
\end{array}} \right|\left( \begin{array}{l}
{\rm{Interchanging }}\,\,I\\
{\rm{and }}\,\,II\,\,{\rm{ columns}}
\end{array} \right)
\end{array}\]
$$\eqalign{
& = - g\left( x \right) \cr
& \Rightarrow g\left( x \right) + g\left( { - x} \right) = 0 \cr} $$
2.
Let $$A$$ and $$B$$ be two symmetric matrices of order 3.
Statement - 1 : $$A(BA)$$ and $$(AB)A$$ are symmetric matrices.
Statement - 2 : $$AB$$ is symmetric matrix if matrix multiplication of $$A$$ with $$B$$ is commutative.
A.
Statement - 1 is true, Statement - 2 is true; Statement - 2 is not a correct explanation for Statement - 1.
B.
Statement - 1 is true, Statement - 2 is false.
C.
Statement - 1 is false, Statement - 2 is true.
D.
Statement - 1 is true, Statement - 2 is true; Statement - 2 is a correct explanation for Statement - 1.
Answer :
Statement - 1 is true, Statement - 2 is true; Statement - 2 is not a correct explanation for Statement - 1.
View Solution
Discuss Question
$$\eqalign{
& \therefore \,\,A' = A,\,\,B' = B \cr
& {\text{Now }}\left( {A\left( {BA} \right)} \right)' = \left( {BA} \right)'A' \cr
& = \left( {A'B'} \right)A' = \left( {AB} \right)A = A\left( {BA} \right) \cr
& {\text{Similarly}}\,\,\left( {\left( {AB} \right)A} \right)' = \left( {AB} \right)A \cr} $$
So, $$A(BA)$$ and $$(AB)A$$ are symmetric matrices.
Again $$(AB)' = B'A’ = BA$$
Now if $$BA = AB,$$ then $$AB$$ is symmetric matrix.
3.
If \[f\left( x \right) = \left[ {\begin{array}{*{20}{c}}
{\cos x}&{ - \sin x}&0 \\
{\sin x}&{\cos x}&0 \\
0&0&1
\end{array}} \right]\] then $$f\left( {x + y} \right)$$ is equal to
A.
$$f\left( x \right) + f\left( y \right)$$
B.
$$f\left( x \right) - f\left( y \right)$$
C.
$$f\left( x \right) \cdot f\left( y \right)$$
D.
None of these
Answer :
$$f\left( x \right) \cdot f\left( y \right)$$
View Solution
Discuss Question
\[f\left( {x + y} \right) = \left[ {\begin{array}{*{20}{c}}
{\cos \left( {x + y} \right)}&{ - \sin \left( {x + y} \right)}&0 \\
{\sin \left( {x + y} \right)}&{\cos \left( {x + y} \right)}&0 \\
0&0&1
\end{array}} \right]\]
\[f\left( {x + y} \right) = \left[ {\begin{array}{*{20}{c}}
{\cos x}&{ - \sin x}&0 \\
{\sin x}&{\cos x}&0 \\
0&0&1
\end{array}} \right]\left[ {\begin{array}{*{20}{c}}
{\cos y}&{ - \sin y}&0 \\
{\sin y}&{\cos y}&0 \\
0&0&1
\end{array}} \right] = f\left( x \right) \cdot f\left( y \right).\]
4.
If $${A_1}{B_1}{C_1},{A_2}{B_2}{C_2}$$ and $${A_3}{B_3}{C_3}$$ are three digit numbers, each of which is divisible by $$k,$$ then \[\Delta = \left| {\begin{array}{*{20}{c}}
{{A_1}}&{{B_1}}&{{C_1}}\\
{{A_2}}&{{B_2}}&{{C_2}}\\
{{A_3}}&{{B_3}}&{{C_3}}
\end{array}} \right|\] is
A.
divisible by $$k$$
B.
divisible by $$k^2$$
C.
divisible by $$k^3$$
D.
None of these
Answer :
divisible by $$k$$
View Solution
Discuss Question
Since, $${A_1}{B_1}{C_1},{A_2}{B_2}{C_2}$$ and $${A_3}{B_3}{C_3}$$ are divisible by $$k,$$ therefore; $$100{A_1} + 10{B_1} + {C_1} = {n_1}k;100{A_2} + 10{B_2} + {C_2} = {n_2}k;100{A_3} + 10{B_3} + {C_3} = {n_3}k$$
(where $${n_1} , {n_2} , {n_3}$$ are integers)
Now, \[\Delta = \left| {\begin{array}{*{20}{c}}
{{A_1}}&{{B_1}}&{{C_1}}\\
{{A_2}}&{{B_2}}&{{C_2}}\\
{{A_3}}&{{B_3}}&{{C_3}}
\end{array}} \right|\]
\[\begin{array}{l}
= \left| {\begin{array}{*{20}{c}}
{{A_1}}&{{B_1}}&{100{A_1} + 10{B_1} + {C_1}}\\
{{A_2}}&{{B_2}}&{100{A_2} + 10{B_2} + {C_2}}\\
{{A_3}}&{{B_3}}&{100{A_3} + 10{B_3} + {C_3}}
\end{array}} \right|\left[ {{\rm{Applying, }}{C_3} \to {C_3} + 10{C_2} + 100{C_1}} \right]\\
= \left| {\begin{array}{*{20}{c}}
{{A_1}}&{{B_1}}&{{n_1}k}\\
{{A_2}}&{{B_2}}&{{n_2}k}\\
{{A_3}}&{{B_3}}&{{n_3}k}
\end{array}} \right| = k\left| {\begin{array}{*{20}{c}}
{{A_1}}&{{B_1}}&{{n_1}}\\
{{A_2}}&{{B_2}}&{{n_2}}\\
{{A_3}}&{{B_3}}&{{n_3}}
\end{array}} \right| = k{\Delta _1}
\end{array}\]
⇒ $$\Delta$$ is divisible by $$k$$
[Since, elements of $$\Delta_1$$ are integers ∴ $$\Delta_1$$ is an integer.]
5.
Let \[\Delta = \left| {\begin{array}{*{20}{c}}
{1 + {x_1}{y_1}}&{1 + {x_1}{y_2}}&{1 + {x_1}{y_3}}\\
{1 + {x_2}{y_1}}&{1 + {x_2}{y_2}}&{1 + {x_2}{y_3}}\\
{1 + {x_3}{y_1}}&{1 + {x_3}{y_2}}&{1 + {x_3}{y_3}}
\end{array}} \right|,\] then value of $$\Delta $$ is
A.
$${x_1}{x_2}{x_3} + {y_1}{y_2}{y_3}$$
B.
$${x_1}{x_2}{x_3}{y_1}{y_2}{y_3}$$
C.
$${x_2}{x_3}{y_2}{y_3} + {x_3}{x_1}{y_3}{y_1} + {x_1}{x_2}{y_1}{y_2}$$
D.
$$0$$
Answer :
$$0$$
View Solution
Discuss Question
We can write $$\Delta = {\Delta _1} + {y_1}{\Delta _2},{\text{ where}}$$
\[\begin{array}{l}
{\Delta _1} = \left| {\begin{array}{*{20}{c}}
1&{1 + {x_1}{y_2}}&{1 + {x_1}{y_3}}\\
1&{1 + {x_2}{y_2}}&{1 + {x_2}{y_3}}\\
1&{1 + {x_3}{y_2}}&{1 + {x_3}{y_3}}
\end{array}} \right|{\rm{ and}}\\
{\Delta _2} = \left| {\begin{array}{*{20}{c}}
{{x_1}}&{1 + {x_1}{y_2}}&{1 + {x_1}{y_3}}\\
{{x_2}}&{1 + {x_2}{y_2}}&{1 + {x_2}{y_3}}\\
{{x_3}}&{1 + {x_3}{y_2}}&{1 + {x_3}{y_3}}
\end{array}} \right|
\end{array}\]
$$\eqalign{
& {\text{In }}{\Delta _1},{\text{use }}{C_2} \to {C_2} - {C_1}{\text{ and }}{C_3} \to {C_3} - {C_1} \cr
& {\text{so that,}} \cr} $$
\[{\Delta _1} = \left| {\begin{array}{*{20}{c}}
1&{{x_1}{y_2}}&{{x_1}{y_3}}\\
1&{{x_2}{y_2}}&{{x_2}{y_3}}\\
1&{{x_3}{y_2}}&{{x_3}{y_3}}
\end{array}} \right| = 0\]
$$\eqalign{
& \left[ {\because {C_2}{\text{ and }}{C_3}{\text{ are proportional}}} \right] \cr
& {\text{In }}{\Delta _2},{\text{us }}{C_2} \to {C_2} - {y_2}{C_1} \cr
& {\text{and }}{C_3} \to {C_3} - {y_3}{C_1}{\text{ to get}} \cr} $$
\[{\Delta _2} = \left| {\begin{array}{*{20}{c}}
{{x_1}}&1&1 \\
{{x_2}}&1&1 \\
{{x_3}}&1&1
\end{array}} \right| = 0\left[ {\because {C_2}{\text{ and }}{C_3}{\text{ are identical}}} \right]\]
$$\therefore \Delta = 0$$
6.
If $$a \ne p,b \ne q,c \ne r$$ and \[\left| {\begin{array}{*{20}{c}}
p&b&c\\
a&q&c\\
a&b&r
\end{array}} \right| = 0\] then the value of $$\frac{p}{{p - a}} + \frac{q}{{q - b}} + \frac{r}{{r - c}}$$ is equal to
A.
$$ - 1$$
B.
$$1$$
C.
$$ - 2$$
D.
$$2$$
Answer :
$$2$$
View Solution
Discuss Question
Given \[\left| {\begin{array}{*{20}{c}}
p&b&c\\
a&q&c\\
a&b&r
\end{array}} \right| = 0\]
$${R_1} \to {R_1} - {R_2},{R_2} \to {R_2} - {R_3}$$ reduces the determinant to
\[\left| {\begin{array}{*{20}{c}}
{p - a}&{b - q}&0\\
0&{q - b}&{c - r}\\
a&b&r
\end{array}} \right| = 0\]
$$ \Rightarrow \,\left( {p - a} \right)\left( {q - b} \right)r + a\left( {b - q} \right)\left( {c - r} \right) - b\left( {p - a} \right)\left( {c - r} \right) = 0$$
$$ \Rightarrow $$ Dividing throughout by $$\left( {p - a} \right)\left( {q - b} \right)\left( {r - c} \right),$$ we get
$$\eqalign{
& \Rightarrow \,\frac{r}{{r - c}} + \frac{a}{{p - a}} + \frac{b}{{q - b}} = 0 \cr
& \Rightarrow \,\frac{r}{{r - c}} + \frac{a}{{p - a}} + \frac{b}{{q - b}} = 2 \cr} $$
7.
If \[y = \left| {\begin{array}{*{20}{c}}
{\sin x}&{\cos x}&{\sin x}\\
{\cos x}&{ - \sin x}&{\cos x}\\
x&1&1
\end{array}} \right|\] then $$\frac{{dy}}{{dx}}$$ is
A.
1
B.
2
C.
3
D.
0
Answer :
1
View Solution
Discuss Question
\[\begin{array}{l}
\frac{{dy}}{{dx}} = \left| {\begin{array}{*{20}{c}}
{\cos x}&{ - \sin x}&{\cos x}\\
{\cos x}&{ - \sin x}&{\cos x}\\
x&1&1
\end{array}} \right| + \left| {\begin{array}{*{20}{c}}
{\sin x}&{\cos x}&{\sin x}\\
{ - \sin x}&{ - \cos x}&{ - \sin x}\\
x&1&1
\end{array}} \right| + \left| {\begin{array}{*{20}{c}}
{\sin x}&{\cos x}&{\sin x}\\
{\cos x}&{ - \sin x}&{\cos x}\\
1&0&0
\end{array}} \right|\\
= 0 - \left| {\begin{array}{*{20}{c}}
{\sin x}&{\cos x}&{\sin x}\\
{\sin x}&{\cos x}&{\sin x}\\
x&1&1
\end{array}} \right| + 1\left| {\begin{array}{*{20}{c}}
{\cos x}&{\sin x}\\
{ - \sin x}&{\cos x}
\end{array}} \right|
\end{array}\]
$$ = 0 + \left( {{{\cos }^2}x + {{\sin }^2}x} \right)$$
8.
If \[A = \left[ {\begin{array}{*{20}{c}}
1&2\\
0&3
\end{array}} \right]\] is a $$2 \times 2$$ matrix and $$f\left( x \right) = {x^2} - x + 2$$ is a polynomial, then what is $$f\left( A \right) \,? $$
A.
\[\left[ {\begin{array}{*{20}{c}}
1&7\\
1&7
\end{array}} \right]\]
B.
\[\left[ {\begin{array}{*{20}{c}}
2&6\\
0&8
\end{array}} \right]\]
C.
\[\left[ {\begin{array}{*{20}{c}}
2&6\\
0&6
\end{array}} \right]\]
D.
\[\left[ {\begin{array}{*{20}{c}}
2&6\\
0&7
\end{array}} \right]\]
Answer :
\[\left[ {\begin{array}{*{20}{c}}
2&6\\
0&8
\end{array}} \right]\]
View Solution
Discuss Question
Given that, \[A = \left[ {\begin{array}{*{20}{c}}
1&2\\
0&3
\end{array}} \right]\]
\[{A^2} = \left[ {\begin{array}{*{20}{c}}
1&2\\
0&3
\end{array}} \right]\left[ {\begin{array}{*{20}{c}}
1&2\\
0&3
\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}
1&{2 + 6}\\
0&9
\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}
1&8\\
0&9
\end{array}} \right]\]
Since, $$f\left( x \right) = {x^2} - x + 2$$
Putting $$A$$ in place of $$x$$
$$f\left( A \right) = {A^2} - A + 2I$$
\[\begin{array}{l}
= \left[ {\begin{array}{*{20}{c}}
1&8\\
0&9
\end{array}} \right] - \left[ {\begin{array}{*{20}{c}}
1&2\\
0&3
\end{array}} \right] + \left[ {\begin{array}{*{20}{c}}
2&0\\
0&2
\end{array}} \right]\\
= \left[ {\begin{array}{*{20}{c}}
{1 - 1 + 2}&{8 - 2 + 0}\\
{0 - 0 + 0}&{9 - 3 + 2}
\end{array}} \right]\\
= \left[ {\begin{array}{*{20}{c}}
2&6\\
0&8
\end{array}} \right]
\end{array}\]
9.
If $$A = {\left[ {{a_{ij}}} \right]_{n \times n}}$$ be a diagonal matrix with diagonal
element all different and $$B = {\left[ {{a_{ij}}} \right]_{n \times n}}$$ be some
another matrix. Let $$AB = {\left[ {{c_{ij}}} \right]_{n \times n}}$$ then $$c_{ij}$$ is equal to
A.
$${a_{jj}}{b_{ij}}$$
B.
$${a_{ii}}{b_{ij}}$$
C.
$${a_{ij}}{b_{ij}}$$
D.
$${a_{ij}}{b_{ji}}$$
Answer :
$${a_{ii}}{b_{ij}}$$
View Solution
Discuss Question
$${c_{ij}} = \sum\limits_{k = 1}^n {{a_{ik}}{b_{kj}}} \,\,\,\left( {{\text{In general}}} \right)$$
and in a diagonal matrix non-diagonal elements are zero
i.e., \[{a_{ij}} = \left\{ \begin{gathered}
0,\,\,{\text{if }}i \ne j \hfill \\
{a_{ii}}{\text{, if }}i = j \hfill \\
\end{gathered} \right.\]
So, $${c_{ij}} = {a_{ii}}{b_{ij}}$$
10.
The values of $$a, b, c$$ if \[\left[ {\begin{array}{*{20}{c}}
0&{2b}&c\\
a&b&{ - c}\\
a&{ - b}&c
\end{array}} \right]\] is orthogonal are
A.
$$a = \pm \frac{1}{{\sqrt 2 }};b = \pm \frac{1}{{\sqrt 6 }};c = \pm \frac{1}{{\sqrt 3 }}$$
B.
$$a = \pm \frac{1}{{\sqrt 2 }};b = \pm \frac{1}{{\sqrt 3 }};c = \pm \frac{1}{{\sqrt 6 }}$$
C.
$$a = \pm \frac{1}{{\sqrt 6 }};b = \pm \frac{1}{{\sqrt 2 }};c = \pm \frac{1}{{\sqrt 3 }}$$
D.
$$a = \pm \frac{1}{{\sqrt 3 }};b = \pm \frac{1}{{\sqrt 2 }};c = \pm \frac{1}{{\sqrt 6 }}$$
Answer :
$$a = \pm \frac{1}{{\sqrt 2 }};b = \pm \frac{1}{{\sqrt 6 }};c = \pm \frac{1}{{\sqrt 3 }}$$
View Solution
Discuss Question
Let, \[A = \left[ {\begin{array}{*{20}{c}}
0&{2b}&c\\
a&b&{ - c}\\
a&{ - b}&c
\end{array}} \right]\]
Now, \[{A^T} = \left[ {\begin{array}{*{20}{c}}
0&a&a\\
{2b}&b&{ - b}\\
c&{ - c}&c
\end{array}} \right]\]
∵ $$A$$ is orthogonal
∴ $$A{A^T} = I$$
\[ \Rightarrow \left[ {\begin{array}{*{20}{c}}
0&{2b}&c\\
a&b&{ - c}\\
a&{ - b}&c
\end{array}} \right]\left[ {\begin{array}{*{20}{c}}
0&a&a\\
{2b}&b&{ - b}\\
c&{ - c}&c
\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}
1&0&0\\
0&1&0\\
0&0&1
\end{array}} \right]\]
Equating the corresponding elements, we get,
$$4{b^2} + {c^2} = 1\,\,\,\,.....\left( 1 \right)$$
$$\eqalign{
& 2{b^2} - {c^2} = 0\,\,\,\,.....\left( 2 \right) \cr
& {a^2} + {b^2} + {c^2} = 1\,\,\,\,.....\left( 3 \right) \cr} $$
On solving (1), (2) and (3), we get,
$$a = \pm \frac{1}{{\sqrt 2 }};b = \pm \frac{1}{{\sqrt 6 }};c = \pm \frac{1}{{\sqrt 3 }}$$