# How do you use the factor theorem to determine whether x-5 is a factor of #3x^2 + 7x + 40#?

##### 1 Answer

Jan 10, 2016

Substitute

#### Explanation:

If

We find:

#f(5) = 3*5^2+7*5+40 = 75+35+40 = 150 != 0#

So

In fact we can tell that

#Delta = b^2-4ac = 7^2-(4*3*40) = 49-480 = -431#