RS Aggarwal

### Express the vector as sum of two vectors such that one is parallel to the vector and the other is perpendicular to .

Solution: $\begin{array}{l} \vec{a}=6 \hat{\imath}-3 \hat{\jmath}-6 \hat{k} \\ \vec{b}=\hat{\imath}+\hat{\jmath}+\hat{k} \end{array}$ Let $\vec{a}$ be written as sum of $\vec{c}+\vec{d}$, where...

### Show that the vector is equally inclined to the coordinate axes.

Solution: $\begin{array}{l} \vec{a}=\cos \gamma=\frac{1}{\sqrt{3}} \\ \mathrm{I} \vec{a} \mathrm{I}=\sqrt{1^{2}+1^{2}+1^{2}}=\sqrt{3} \end{array}$ Since direction cosines or cosines of angle made by...

### Find the position vector of the mid-point of the vector joining the points and

Solution: $\begin{array}{l} \overrightarrow{O A}=3 \hat{\imath}+2 \hat{\jmath}+6 \hat{k} \\ \overrightarrow{O B}=\hat{\imath}+4 \hat{\jmath}-2 \hat{k} \end{array}$ Let $\mathrm{C}$ be the mid-point...

### Find the position vector of a point which divides the line joining and in the ratio (i) internally (ii) externally.

Solution: $\begin{array}{l} \overrightarrow{O A}=-2 \hat{\imath}+\hat{\jmath}+3 \hat{k} \\ \overrightarrow{O B}=3 \hat{\imath}+5 \hat{\jmath}-2 \hat{k} \end{array}$ (i) $\mathrm{R}$ divides...

### The position vectors of two points and are and respectively. Find the position vector of a point which divides externally in the ratio . Also, show that is the mid-point of the line segment .

Solution: Given: $\overrightarrow{O A}=(2 \vec{a}+\vec{b})$ $\overrightarrow{O B}=(\vec{a}-3 \vec{b})$ Position vector of $\mathrm{C}$ which divides $\mathrm{AB}$ in the ratio $1: 2$ externally is...

### Find the position vector of the point which divides the join of the points and (i) internally and (ii) externally in the ratio

Solution: Given: $\overrightarrow{O A}=(2 \vec{a}-3 \vec{b})$ $\overrightarrow{O B}=(3 \vec{a}-2 \vec{b})$ (i) Let $\mathrm{P}$ be the point that divides $\mathrm{A}, \mathrm{B}$ internally in the...

### Mark (√) against the correct answer in the following: The general solution of the DE is A. B. C. D. None of these

Solution: $\log \left(\frac{d y}{d x}\right)=(a x+b y)$ $\begin{array}{l} \frac{d y}{d x}=e^{a x+b y} \\ \frac{d y}{e^{b y}}=e^{a x} d x \end{array}$ On integrating on both sides we get...

### Mark (√) against the correct answer in the following: The general solution of the is A. B. C. D. None of these

Solution: $\begin{array}{r} x \sqrt{1+y^{2}} \mathrm{dx}+\mathrm{y} \sqrt{1+x^{2}} \mathrm{dy}=0 \\ \frac{y d y}{\sqrt{1+y^{2}}}=\frac{-x d x}{\sqrt{1+x^{2}}} \end{array}$ Let $1+y^{2}=t$ and...

### Mark (√) against the correct answer in the following: the solution of the DE is A. B. C. D. none of these

Solution: $\begin{array}{l} x \operatorname{Cosydy}=\left(x e^{x} \log x+e^{x}\right) d x \\ \operatorname{Cosydy}=\frac{x \operatorname{exlogx}+e x}{x} d x \end{array}$ On integrating on both sides...

### Mark (√) against the correct answer in the following: The solution of the is A. B. C. D. none of these

Solution: $\cos x(1+\cos y) d x-\sin y(1+\sin x) d y=0$ Let $1+\cos y=t$ and $1+\sin x=u$ On differentiating both equations, we get $-\sin y d y=d t$ and $\cos x d x=d u$ Substitute this in the...

### Mark (√) against the correct answer in the following: The solution of the is A. B. C. D. None of these

Solution: $x \frac{d y}{d x}=\cot y$ Separating the variables, we get, $\begin{array}{c} \frac{d y}{\cot y}=\frac{d x}{x} \\ \tan y d y=\frac{d x}{x} \end{array}$ Integrating both sides, we get,...

### Find the general solution for each of the following differential equations.

Solution: $\frac{d y}{d x}=\operatorname{ytan} x-2 \sin x-\ldots(1)$ General solution for the differential equation in the form of $\frac{d y}{d x}+\mathrm{Py}=\mathrm{Q}$ General solution is given...

### Find the general solution for each of the following differential equations.

Solution: $\frac{d y}{d x}+2 y=\sin x- \dots(1)$ General solution for the differential equation in the form of is given by, $y \cdot(I . F .)=\int Q \cdot(I . F .) d x+c$ Where, integrating factor,...

### Find the general solution for each of the following differential equations.

Solution: $x d y+\left(y-x^{3}\right) d x=0\dots (1)$ General solution for the differential equation in the form of is given by,$\frac{d y}{d x}+P y=Q$ $y \cdot(I . F .)=\int Q \cdot(I . F .) d x+c$...

### Find the general solution for each of the following differential equations.

Solution: $\begin{array}{r} x \frac{d y}{d x}+2 y=x^{2} \log x-\ldots(1) \\ \qquad \frac{d(\log x)}{d x}=\frac{1}{x} \end{array}$ General solution for the differential equation in the form of...

### If the matrix A is both symmetric and skew-symmetric, show that A is a zero matrix.

Solution: The transpose of the matrix is an operation of making interchange of elements by the rule on positioned element $a_{j i}$ shifted to new position $a_{j i}$. The symmetric matrix is defined...

### If and , find .

Solution: We have $A=\left(\begin{array}{ll}2 & 3 \\ 1 & 2\end{array}\right)$. Now addition/subtraction of two matrices is possible if order of both the matrices are same and multiplication...

### If A and B are symmetric matrices of the same order, show that (AB – BA) is a skew symmetric matrix.

Solution: We have $A$ and $B$ are symmetric matrices. Therefore $A^{T}=A$ and $B^{T}=B$ The transpose of the matrix is an operation of making interchange of elements by the rule on positioned...

### If , show that .

Solution: We have $A=\left(\begin{array}{cc}\cos \alpha & \sin \alpha \\ -\sin \alpha & \cos \alpha\end{array}\right)$. The transpose of the matrix is an operation of making interchange of...

### If and , find a matrix such that

Solution: We have $A=\left(\begin{array}{ll}4 & 2 \\ 1 & 3\end{array}\right), B=\left(\begin{array}{cc}-2 & 1 \\ 3 & 2\end{array}\right)$ and $3 A-2 B+X=0$ We can have the addition...

### If and , find a matrix such that .

Solution: We have $A=\left(\begin{array}{cc}2 & -3 \\ 4 & 5\end{array}\right), B=\left(\begin{array}{cc}-1 & 2 \\ 0 & 3\end{array}\right)$ and $A+2 B+X=0$. We can have the addition...

### If , show that is symmetric

Solution: We have $\left(\begin{array}{ll}4 & 5 \\ 1 & 8\end{array}\right)$. The transpose of the matrix is an operation of making interchange of elements by the rule on positioned element...

### Find the value of and for which

Solution: We have $\left(\begin{array}{cc}x & y \\ 3 y & x\end{array}\right)\left(\begin{array}{l}1 \\ 2\end{array}\right)=\left(\begin{array}{l}3 \\ 5\end{array}\right)$. Use the...

### Find the value of and for which

Solution: We have $\left(\begin{array}{cc}2 & -3 \\ 1 & 1\end{array}\right)\left(\begin{array}{l}x \\ y\end{array}\right)=\left(\begin{array}{l}1 \\ 3\end{array}\right)$. Use the...

### If then find the least value of for which .

Solution: We have $A=\left(\begin{array}{cc}\cos \alpha & -\sin \alpha \\ \sin \alpha & \cos \alpha\end{array}\right)$ Use the addition rule and get $A+A^{T}=I_{2}$ as follow:...

### If and , find the matrix such that is a zero matrix

Solution: We have $A=\left(\begin{array}{cc}1 & -5 \\ -3 & 2 \\ 4 & -2\end{array}\right) ; B=\left(\begin{array}{cc}3 & 1 \\ 2 & -1 \\ -2 & 3\end{array}\right) .$ and...

### If , find the values of .

Solution: We have $\left(\begin{array}{cc}x & 3 x-y \\ 2 x+z & 3 y-w\end{array}\right)=\left(\begin{array}{ll}3 & 2 \\ 4 & 7\end{array}\right)$. Now from the equality of matrices we...

### If , find the values of and .

Solution: We have $x\left(\begin{array}{l}2 \\ 3\end{array}\right)+y\left(\begin{array}{c}-1 \\ 1\end{array}\right)=\left(\begin{array}{c}10 \\ 5\end{array}\right)$. Use the addition rule and get...

### Express the matrix as sum af two matrices such that and is symmetric and the other is skew-symmetric.

Solution: Given that $A=\left[\begin{array}{lll}3 & 2 & 5 \\ 4 & 1 & 3 \\ 0 & 6 & 7\end{array}\right]$, to express as sum of symmetric matrix $P$ and skew symmetric matrix...

### Express the matrix as the sum of a symmetric matrix and a skew-symmetric matrix.

Solution: Given that $\mathrm{A}=\left[\begin{array}{rr}3 & -4 \\ 1 & -1\end{array}\right]$,to express as the sum of symmetric matrix $\mathrm{P}$ and skew symmetric matrix Q. $A=P+Q$ Where...

### If , show that

Solution: We have $\boldsymbol{F}(\boldsymbol{X})=\left(\begin{array}{ccc}\cos x & -\sin x & 0 \\ \sin x & \cos x & 0 \\ 0 & 0 & 1\end{array}\right)$ and to show...

### Compute AB and BA, which ever exists when

Solution: We have $\boldsymbol{A}=\left(\begin{array}{ccc}\mathbf{0} & \mathbf{1} & -\mathbf{5} \\ \mathbf{2} & \mathbf{4} & \mathbf{0}\end{array}\right)$ and...

### Compute AB and BA, which ever exists when

Solution: We have $\boldsymbol{A}=\left(\begin{array}{cc}-\mathbf{1} & \mathbf{1} \\ -\mathbf{2} & \mathbf{2} \\ -\mathbf{3} & \mathbf{3}\end{array}\right)$ and...

### Compute AB and BA, which ever exists when

Solution: We have $\boldsymbol{A}=\left(\begin{array}{cc}\mathbf{2} & \mathbf{- 1} \\ \mathbf{3} & \mathbf{0} \\ \mathbf{- 1} & \mathbf{4}\end{array}\right)$ and...

### If then write the value of

Solution: $\text { If }\left[\begin{array}{ll} a & b \\ c & d \end{array}\right]=\left[\begin{array}{ll} e & f \\ g & h \end{array}\right]$ Therefore $a=e, b=f, c=g, d=h$ It is given...

### Find matrix , if

Solution: It is given that $\left[\begin{array}{ccc}3 & 5 & -9 \\ -1 & 4 & -7\end{array}\right]+x=\left[\begin{array}{lll}6 & 2 & 3 \\ 4 & 8 & 6\end{array}\right]$...

### Mark (√) against the correct answer in the following: Let . Then, dom (f) and range (f) are respectively A. and B. and C. R and R + D. and

Solution: Option(A) is correct. $f(x)=x^{3}$ $f(x)$ can assume any value, therefore domain of $f(x)$ is $R$ Range of the function can be positive or negative Real numbers, as the cube of any number...

Solution: Option(C) is correct. $f(x)=\sqrt{\log \left(2 x-x^{2}\right)}$ For $f(x)$ to be defined $2 x-x^2$ should be positive. Solving inequality, (Log taken to the opposite side of the equation...
Solution: Option(B) is correct. $\begin{array}{l} \mathrm{f}(\mathrm{x})=\cos ^{-1}(3 \mathrm{x}-1) \end{array}$ Domain for function $\cos ^{-1} \mathrm{x}$ is $[-1,1]$ and range is $[0, \pi]$ When...