Question

Which equation, when graphed, has x-intercepts at (−1, 0) and (−5, 0) and a y-intercept at (0, −30)? f(x) = −6(x 1)(x 5) f(x) = −6(x − 1)(x − 5) f(x) = −5(x 1)(x 5) f(x) = −5(x − 1)(x − 5).

Answer 1

f(x) = −6(x+ 1)(x +5)

Explanation:

x-intercepts at (−1, 0) and (−5, 0)

so the roots are -1 and -5 (where the graph intersects the x-axis)

this will give us that f(x) = (x- root1)(x-root2) = (x- -1)(x- -5) = (x+1)(x+5)

y-intercept at (0, −30) is telling us that when x= 0 the y = -30

y = a ( x+1)(x+5) , in general

y = a(0+1)(0+5), is the equation if x=0

-30 = a·1·5, we need y= -30 when x= 0

-30 = 5a , divide both sides of the equation by 5

-6 = a

The correct choice is :

f(x) = −6(x+ 1)(x +5)

f(x) = −6(x − 1)(x − 5)

f(x) = −5(x +1)(x +5)

f(x) = −5(x − 1)(x − 5).