Answer:
f(x) = (x + 3)² - 13
Step-by-step explanation:
The equation of a parabola in vertex form is
f(x) = a(x - h)² + k
Given
f(x) = x² + 6x - 4
Using the method of completing the square
add/subtract ( half the coefficient of the x- term )² to x² + 6x
f(x) = x² + 2(3)x + 9 - 9 - 4
f(x) = (x + 3)² - 13 ← in vertex form
