Question

Factorise x^2+9x+18 and hence solve x^2+9x+18=0

Answer 1

$x^2+9x+18\\\\9x=3x+6x\\18=3\cdot6\\\\x^2+9x+18=x^2+3x+6x+18=x(x+3)+6(x+3)=(x+3)(x+6)\\\\x^2+9x+18=0\iff(x+3)(x+6)=0\iff x+3=0\ or\ x+6=0\\\\x=-3\ or\ x=-6$