Trig Proof Help! (1 Viewer)

[xokki]

Hi, can anyone help me prove this?

sin(A)cos(A)sin(2A)=1/4(1-cos4A)

 

[Drongoski]

 

[MilkDrinker]

 

[xokki]

Milk drinker, the proof on the RHS is 1/4(1-cos4A) rather than 1/4(1-cos2A) and drongonski, could you elaborate how you got to step 4? I don't really get it

 

[asianese]

 

[xokki]

thanks

 

[asianese]

Does it matter?

 

[MilkDrinker]

sorry, typo in the first line {as you said, it should be cos4A not cos2A}, but after that it should be alright.
I used the identity that
cos(2x)=1-2sin^2(x)
hence:
cos(4x)=1-2sin^2(2x)

please correct me if I have done something wrong in the rest

btw, does anyone know how to get rid of the br thing that comes up on the left of the LaTeX writing?
Thanks