Hi Guys,

 

Just started teaching myself FP2 from home so I might end up with a lot of these....

 

 

anyway im trying to integrate sin5xcos2x dx but am running out of ideas.

 

Ive tried to get everything into 2x's but each time I end up with something wierd.

 

Any ideas?

Looks to me like you need a trig identity!

 

Do you know sin(x+y)= sin(x)cos(y)+ cos(x)sin(y)?

If you replace y with -y that becomes sin(x-y)= sin(x)cos(y)- cos(x)sin(y) because cos(-y)= cos(y) and sin(-y)= -sin(y).

 

Adding those two equations, 2sin(x)cos(y)= sin(x+y)+ sin(x-y) or

sin(x)cos(y)= (sin(x+y)+ sin(x-y))/2.

Now what does that give you for sin(5x)cos(2x)?

Cheers for the help, it worked.