Friday, 25 September 2015

trigonometry - Show that sin2thetacdotcos2theta=(1/8)[1cos(4theta)].

I have these two problems I'm working on!



First of the Double Angle Formula! This formula I attempted to do a lot but couldn't get to the identity!
sin2θcos2θ=18[1cos(4θ)]



For Above question you can only use the following:

sin2θ=12(1cos(2θ))cos2θ=12(1+cos(2θ))



And lastly this Sum And Difference Formula! I tried this one so much, I'm leaning toward it being impossible (it's obviously not.... because it's a question):
cos(ab)cos(a+b)=(cos2asin2b).

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