Integration!

[legacyofpiracy]

Hello, I was reviewing some problems we had done in class and I was getting confused on this particular problem.

S 9sin^2 x cosx dx

Supposedly I am supposed to get 1*arctan(x^2)+C for my answer, but I am having trouble getting there. Should I be using integration by parts or is there a particular formula that applies?

 

[Daniel_Feldman]

Hello, I was reviewing some problems we had done in class and I was getting confused on this particular problem.

S 9sin^2 x cosx dx

Supposedly I am supposed to get 1*arctan(x^2)+C for my answer, but I am having trouble getting there. Should I be using integration by parts or is there a particular formula that applies?

Huh?

Are you sure that's the right answer? It shouldn't be....

u=sinx

du=cosxdx



so we have 9 S u^2du

=9(u^3/3)=3sin^3(x)+C

 

[legacyofpiracy]

oh wow your right. Hmm I don't know how I got that answer then, it makes alot more sense now...thanks! :roll:

 

[Unco]

Just watch that the derivative of sin(x) is +cos(x).

 

[Daniel_Feldman]

Yep. Sorry about that.