# How do you factor and solve #x^2-4x-21=0#?

##### 1 Answer

May 27, 2016

3, and -7

#### Explanation:

First factor the trinomial

Find 2 numbers knowing sum (-4) and product (c = - 21). They are the numbers in the factor pair (3, -7).

y = (x + 3)(x - 7)

Solving the 2 binomials, we get:

x = -3 and x = 7