Please HELP with this question?

0 ⤊

On what interval is f(x) = 3/(x^2 + 8x + 15) decreasing?

a) -5 < x < -3
b) x < -4
c) -4 < x < -3 and x > -3
d) x < -5 and x > -3

2007-05-17 06:15:11 · 3 answers · asked by James P 1 in Science & Mathematics ➔ Mathematics

с)
f(x) = 3/(x^2 + 8x + 15) =>
f' = -3*(2x+8)/(x^2 + 8x + 15)^2
If f' < 0 then f is decreasing. So c) is the correct answer

2007-05-17 06:27:52 · answer #1 · answered by Evgeniy E 3 · 0⤊ 0⤋

f(x) = 3 / (x + 5).(x + 3)
Vertical asymptotes are x = - 5 and x = - 3
f(x) is decreasing for x < - 5 and x > - 3
Answer d)

2007-05-17 17:42:02 · answer #2 · answered by Como 7 · 0⤊ 1⤋

Take the derivative to find out where f ' (x) = 0 (if anywhere). Then find the range where f ' (x) > 0.

2007-05-17 13:28:38 · answer #3 · answered by Anonymous · 0⤊ 1⤋