Question

Explain why...
x2 + 7x + 8

does not factorise

Answer 1

Explanation:

if a quadratic of this form can be factorised the factors are

(x + a)(x + b).

In this case a*b would be = + 8 and a + b would be + 7.

There are no integer values which will give these 2 results so x^2 + 7x + 8 cannot be factorised.

An example of a quadratic that can be factories is x^2 + 8x + 7,

because ab = 7 *1 and a + b = 7 + 1 = 8 so the factors are:

(x + 1)(x + 7).

Answer 2

Explanation:

because you need 2 numbers that

(+)=7

and

(x)=8

no 2 whole numbers work

it will have to be decimals

so you can't factorise

so you have to use the quadratic formula

hope this helps :)