Simple integration but i forgot how to do it

[mr_coffee]

Here is my work and problem:

i made an sign mistake, d/dt (cos t) = -sin(t).http://img101.imageshack.us/img101/561/blah4gk.jpg

 

[Fermat]

There's a problem with the link.

I get document not found

 

[mr_coffee]

Ahh sorry!
http://img101.imageshack.us/img101/561/blah4gk.jpg

 

[TD]

That seems correct, what's the problem? You only forgot the unit vector j I believe.

 

[mr_coffee]

oh sorry, i got that answer from someone, but didn't know how they got it! the parts i were i let u = cos (PI t);
du = -PIsin(PI t);
-1/PI de = sin(PI t);
but i don't know how that helps me when i plug it back in!

 

[TD]

Just integrate each component. Pi is just a constant, you don't even need a real substitution for it. Do it indirectly by adjusting the dt and correcting in front of the integral.

\int {\cos \left( {\pi t} \right)dt} = \frac{1}<br /> {\pi }\int {\cos \left( {\pi t} \right)d\left( {\pi t} \right)} = \frac{{\sin \left( {\pi t} \right)}}<br /> {\pi } + C

 

[mr_coffee]

OHh! i was making that way more complicated then it should havve been! thanks again TD! :D

 

[TD]

No problem