• # question_answer                        Factorise the following : (a) $18+11x+{{x}^{2}}$ (b) ${{y}^{2}}-2y-15$

 (a)    $18+\text{11}x+{{x}^{2}}=\text{ }{{x}^{2}}+1\text{1}x+18$ $={{x}^{2}}+\left( 9+2 \right)\text{ }x+18$ $={{x}^{2}}+9x+2x+18$ $=x(x+9)+2(x+9)$ = (x + 9) (x + 2) (b)  ${{y}^{2}}-2y-15={{y}^{2}}-(5-3)y-15$ $={{y}^{2}}-5y+3y-15~$ $=y\left( y-5 \right)+3\left( y-5 \right)$ $=\left( y-5 \right)\left( y+3 \right)$