The value of $\begin{vmatrix}x&x + y&x + y + z\\2x&3x+2y&4x+3y+2z\\3x& 6x+3y& 10x+6y+3z\end{vmatrix}$ is |
0 $x$ $x^2$ $x^3$ |
$x^3$ |
The correct answer is Option (4) → $x^3$ ** Determinant: $\displaystyle D=\begin{vmatrix} x & x+y & x+y+z\\[4pt] 2x & 3x+2y & 4x+3y+2z\\[4pt] 3x & 6x+3y & 10x+6y+3z \end{vmatrix}$ Row operations: $R_{2}\to R_{2}-2R_{1},\ R_{3}\to R_{3}-3R_{1}$ After operations the matrix becomes $\displaystyle \begin{vmatrix} x & x+y & x+y+z\\[4pt] 0 & x & 2x+y\\[4pt] 0 & 3x & 7x+3y \end{vmatrix}$ Expand along first column: $\displaystyle D = x\begin{vmatrix} x & 2x+y\\[4pt] 3x & 7x+3y\end{vmatrix}$ $\displaystyle = x\bigl(x(7x+3y)-(2x+y)(3x)\bigr)$ $\displaystyle = x\bigl(7x^{2}+3xy-6x^{2}-3xy\bigr)=x\cdot x^{2}=x^{3}$ |