Which equation reveals the minimum or maximum value of f (x) without changing the form of the equation?
A) ƒ (c) = (x + 3) (x − 4)
B ƒ (x) = x² − 8x + 15
cƒ(x) = (x + 2)² - 1
D) f(x) = x² + 2x − 1