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

The first one is correct. If you plug zero in for the x's, you will get the y intercept (since the value of x on the y axis is zero). Setting the two factors each to zero and solving you get the x intercepts -1 and -5.

Answer 2

Option A

Explanation:

The equation has x intecepts at -1 and -5.

Hence function would be of the form

a(x+1)(x+5) for some real a.

To find a, let us use y intercept

When x =0 we have y =a(1)(5)

y intercept is given as -30

i.e. 5a = -30

a=-6

So

f(x) = -6(x+1)(x+5)

Option A is the right answer.