Question

Factorise x squared + 7x minus 120

Answer 1

`\huge\boxed{x^2+7x-120=(x+15)(x-8)}`

Explanation:

`x^2+7x-120\\\\\left\{\begin{array}{ccc}a+b=7\\ab=-120\end{array}\right\Rightarrow a=15,\ b=-8`

`x^2+7x-120=x^2+15x-8x-120=x(x+15)-8(x+15)\\\\x^2+7x-120=(x+15)(x-8)`