Question

Consider the function f(x) = x2 + 2x – 15. What are the x-intercepts of the function?

Answer 1

f(x) = x^2 + 2x - 15

You can either factor it or use the quadratic formula.

Factored:
y = x^2 + 2x - 15
(x + 5)(x - 3)
x = -5, 3

Quadratic Formula:
-b +/- √(b^2 - 4ac) / 2a
-2 +/- √(2^2 - 4(-15) / 2
-2 +/- √(4 + 60) / 2
-2 +/- √64 / 2
-2 +/- 8 / 2

-2 + 8 / 2
6/2
3

-2 - 8 / 2
-10/2
-5

x = -5, 3


Using both of these methods, you would get the x-intercepts 3 and -5.

Answer 2

Left x intercept (-5,0)
Right x intercept ( 3,0)