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

May 27, 2016

3, and -7

#### Explanation:

First factor the trinomial
$y = {x}^{2} - 4 x - 21$.
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