Asked by Alessandra
How do you find decreasing intervals of
6x^3-63x^2-144x-2?
I found my increasing intervals from placing the derivatives i just can't seem to solve for the decrease
6x^3-63x^2-144x-2?
I found my increasing intervals from placing the derivatives i just can't seem to solve for the decrease
Answers
Answered by
Steve
f decreasing means f' < 0
f' = 18x^2 - 126x - 144
= 18(x^2-7x-8)
= 18(x+1)(x-8)
Since that is a parabola which open upward, f' is negative between the roots.
f(x) is decreasing on the interval (-1,8)
This can be verified by looking at the graph:
http://www.wolframalpha.com/input/?i=6x^3-63x^2-144x-2
f' = 18x^2 - 126x - 144
= 18(x^2-7x-8)
= 18(x+1)(x-8)
Since that is a parabola which open upward, f' is negative between the roots.
f(x) is decreasing on the interval (-1,8)
This can be verified by looking at the graph:
http://www.wolframalpha.com/input/?i=6x^3-63x^2-144x-2
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