If $X=\left\{x:x^2-12x+20=0\right\}\text{and}Y=\left\{x:x^2+5x-14=0\right\}$  then $X-Y=$

$x\left(x-10\right)-2\left(x-10\right)=0$

$x=2,10$

$\therefore X=\left\{2,10\right\}$

$x^2+5x-14=0$

$x^2+7x-2x-14=0$

$x\left(x+7\right)-2\left(x+7\right)=0$

$x=2,-7$

$\therefore Y=\left\{2,-7\right\}$

$\therefore X-Y=\left\{2,10\right\}-\left\{2,-7\right\}$

$=\left\{10\right\}$