Question

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

Answer 1

3, and -7

Explanation:

First factor the trinomial
`y = x^2 - 4x - 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