ACT Math · Quadratic functions and equations

The function f(x) = 2(x+3)² - 8 has a minimum value of what?

The function f(x)=2(x+3)2−8f(x) = 2(x+3)^2 - 8 has a minimum value of what?

Answer and explanation

Answer: F: -8

The function is in vertex form, a(x−h)2+ka(x-h)^2+k, with a=2a=2, h=−3h=-3, and k=−8k=-8. Since a>0a>0, the parabola opens upward, so its minimum value is the yy-coordinate of the vertex, −8-8, choice F. The squared term 2(x+3)22(x+3)^2 is never negative, so the smallest it can be is 00, giving f=−8f=-8. Choice G (88) has the wrong sign. Choice H (−3-3) is the xx-coordinate of the vertex, where the minimum occurs, not the minimum value. Choice J (33) uses the wrong sign for that xx-coordinate and also confuses it with the minimum value.

More Quadratic functions and equations questions

All Quadratic functions and equations questions

Learn the method behind questions like this one

The ACT Math course teaches each tested skill through lessons, step-by-step solutions to sample problems, the complete study guide and full-length practice tests.