- #1
hamburgler
- 22
- 0
Homework Statement
[tex]\int[/tex]cos3xdx
Homework Equations
cos3x = cos2x * cosx
The Attempt at a Solution
Let u= cos2x
du=(x/2) + (cos2x/4x)
v=-sinx
dv=cosuv-[tex]\int[/tex]vdu
-cos2xsinx - [tex]\int[/tex]-sinx(x/2 + cos2x/4x)dx
-cos2xsinx -[tex]\int[/tex]xsinx/2 + (sinxcos2x/4x)
-cos2xsinx - (1/2)xsinx +(sinxcos2x/4x)
-cos2xsinx -(sinx-xcosx/2) + (sinxcos2x/4x)
...aaaand that's about where I get lost/stuck. i can't figure out how to finish off the problem. i get to the last line on the far right and get confused. any help would be much appreciated.