Question

Which point is an x-intercept of the quadratic function

f(x) = (x – 8)(x + 9)?

(0,8)
(0,–8)
(9,0)
(–9,0)

Answer 1

(–9,0)

Explanation:

f(x) = (x – 8)(x + 9)

= x² + 9x -8x - 72

= x² + x - 72

x-intercept is a coordinate of x axis where a function cuts the x-axis. They are points where y=0 or f(x) = 0.

x² + x - 72 = (x – 8)(x + 9) = 0

∴ x – 8 = 0

x = 8

x + 9 = 0

x = -9

The required points are (8, 0) and (-9, 0).

From the choices given there is only one correct answer. (–9,0)