Question #89cfc

1 Answer
Jul 26, 2017

Answer:

#(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.