Let g(x)= arctan(x^3 + 3x^2 - 9x). Find where g(x) is increasing. I know the values of x which g(x) has a hortizontal tangent are x +-3 and x = 1, but I don't know of I should just graph it or use those to find where it increases.

Mathematics For Machine Technology
8th Edition
ISBN:9781337798310
Author:Peterson, John.
Publisher:Peterson, John.
Chapter58: Achievement Review—section Five
Section: Chapter Questions
Problem 30AR: Determine dimension x to 3 decimal places.
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Let g(x)= arctan(x^3 + 3x^2 - 9x). Find where g(x) is increasing. I know the values of x which g(x) has a hortizontal tangent are x +-3 and x = 1, but I don't know of I should just graph it or use those to find where it increases. 

Expert Solution
Solution:

The function is g(x)=arctan(x3+3x2-9x)

Obtain the derivative:

g'x=ddxarctanx3+3x2-9x=3x2+6x-9x3+3x2-9x2+1

Substitute  x =-3: g'-3=3-32+6-3-9-33+3-32-9-32+1=0

Substitute  x =1: g'1=312+61-913+312-912+1=0

Hence, these values x =-3 and x =1 are critical values.

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ISBN:
9781337798310
Author:
Peterson, John.
Publisher:
Cengage Learning,