Given f (x) = (x - 3) (x + 7), what are the x-intercepts?

We can easily say the x intercepts are + 3 and - 7

Or we can multiply (x-3) * (x+7)

x^2 + 4x - 21 = 0

a = 1 b = 4 c = - 21

We solve with the quadratic equation

x = 3

x = - 7

So that proves our answers are correct.