Verifying Trigonomic Identities

[lucy1234]

Hey,

Can anyone help me solve this equation please?

Thanks

Homework Statement

cos(3θ)=cos³θ-3sin²θcosθ

Homework Equations

cos(u+v) = cosu cosv - sinu sinv
sin2u = 2sinu cosu

The Attempt at a Solution

 

[lucy1234]

I started with taking cosθ out of the equation, but got stuck from there

 

[Mark44]

Hey,

Can anyone help me solve this equation please?

Thanks

Homework Statement

cos(3θ)=cos³θ-3sin²θcosθ

Homework Equations

cos(u+v) = cosu cosv - sinu sinv
sin2u = 2sinu cosu

I would start in on the left side.
cos(3θ) = cos(2θ + θ) = ?

 

[iRaid]

cos3x = cos(2x+x) if that helps.

 

[Mark44]

I would start in on the left side.
cos(3θ) = cos(2θ + θ) = ?

cos3x = cos(2x+x) if that helps.

I think that's pretty much what I said.