Which shows the factored form of x2 - 12x - 45?

(x + 3) (x - 15)

(x - 3) (x - 15)

(x + 3) (x + 15)

(x - 3) (x + 15)

Hi!

(x+a) · (x+b) = x²+xa+xb+ab = x²-12x-45

x² = x²

xa+xb = (a+b) x = - 12x ⇒ (a+b) = - 12

ab = - 45

When (a+b) = - 12 and ab = - 45?

+3-15 = - 12 and (+3) (-15) = - 45

-3-15 = - 18 and (-3) (-15) = + 45

+3+15 = + 18 and (+3) (+15) = + 45

-3+15 = + 12 and (-3+15) = - 45

Answer:

(x+3) (x-15)