Question
Using cofactors of elements of third column, evaluate $\Delta = \left| {\begin{array}{*{20}{c}} 1&x&{yz} \\ 1&y&{zx} \\ 1&z&{xy} \end{array}} \right|$

Answer

$ \Delta=a_{13} A_{13}+a_{23} A_{23}+a_{33} A_{33} $
$ =y z(z-y)+z x(x-z)+x y(y-x) $
$ =y z^2-y^2 z+z x^2-z^2 x+x y^2-x^2 y $
$ =z x^2-x^2 y+x y^2-z^2 x+y z^2-y^2 z $
$ =x^2(z-y)+x\left(y^2-z^2\right)+y z(z-y) $
$ =(z-y)\left[x^2-x(z+y)+y z\right] $
$ =(z-y)\left[x^2-x z-x y+y z\right] $
$ =(z-y)[x(x-y)-z(x-y)] $
$ =(z-y)[(x-y)(x-z)] $
$ =(z-y)(x-y)(x-z)$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free