Open Intervals...PLEASE HELP!!

[nikchic5]

Find the open interval(s) in (0, 4pi) on which f(x)= 9x-7 sinx is concave downward.

Select the correct answer(s).
(pi,2pi)
(0,pi)
(0,4pi)
(2pi,3pi)
(3pi,4pi)
(pi,,3pi)

Thanks so much to anyone who can quickly help me!

 

[stapel]

Find the open interval(s) in (0, 4pi) on which f(x)= 9x-7 sinx is concave downward.

Have you looked at the graph?

Please reply showing (or describing) all the steps you have tried thus far. Thank you.

Eliz.

 

[nikchic5]

yes

yea i llooked at and drew the graph but i still dont see it. thanks so much

 

[stapel]

i llooked at and drew the graph but i still dont see it.

Then follow the usual procedure for finding intervals of concavity: Differentiate twice, set equal to zero, and solve for the inflection points. Then test the intervals to find on which f"(x) is positive and negative (that is, on which f(x) is concave up and concave down, respectively).

If you have difficulty, please reply showing all of your work.

Thank you.

Eliz.

 

[nikchic5]

thanks...

thank you very much