College algebra help

Question

Write an equation for the quadratic function whose graph has a y-intercept at y = 40 and x-intercepts at x = 5 and x = −4.

Answer 1

Hi Carla,

Because 5 and -4 are x-intercepts or zeros, your equation will look like this: f(x) = A (x - 5) (x + 4)

To find A, use the y-intercept: replace f(x) by 40 and x by 0: 40 = A (0 - 5) (0+4)

40 = A (-5)(4)

40 = A (-20)

Divide by -20 on both sides: -2 = A

Therefore, f(x) = -2 (x-5) (x+4)