What is the vertex f (x) = 5x^2+20x-16

F (x) = 5x² + 20x - 16

y = 5 (x² + 4x) - 16

y + 16 = 5 (x² + 4x + __)

perfect square:

x² ⇒ x * x

4x ⇒ 2*2x

2² = 4

y + 16 + 4 = 5 (x² + 4x + 4)

y + 20 = 5 (x+2) ²

(x+2) ² ⇒ (x+2) (x+2) = x (x+2) + 2 (x+2) = x² + 2x + 2x + 4 = x² + 4x + 4

y = 5 (x+2) ² - 20