Question

Question #89cfc

Answer 1

`(a+5)(a-4)`

Explanation:

This is a quadratic equation because it has a power of 2 within it.

When factorising a quadratic of the form `ax^2+bx+c`, you can determine whether it factorises with integers (whole numbers) using the formula `b^2-4ac`. If this is a square number, it will factorise. In this case, `b^2-4ac=1^2-(4times1times-20)` which equals 81 so it will factorise (`9^2=81`).

You need to find factors of `c (-20)` that differ by `b (1)` which are `-4 and 5`.

You can double check this by multiplying out the brackets again to give the original equation.