Mastering Trig: Simplify Equations with Easy Tricks | Learn the Basics

[lemurs]

ok.. title says it all I feeling really stupid right now and seem to be having trouble with elementary stuff here..
given r= sin 3x

dr= cos 3x * 3
dx

i got that . but next step in the equation i am doing is

3cos 3x * cos x

as i said feeling stupid si it

3 cos^2 3x?

 

[Integral]

No.

You can only combine trig functions like that when the arguments are equal.

 

[neutrino]

It's certainly not. If you're in doubt, write it as 3(cos(3x))^2.

To rewrite cos 3x * cos x, employ the identities involving cos(A+B) and cos(A-B).

 

[lemurs]

ok i understna what you wrote neutrino
so i but i got that 3 out front so with the little identity bit wuld it be

3(1/2(cos(a-b)+cos(a+b)))

 

[neutrino]

Yes, if it makes the problem any simpler.