Math

How do I go about proving that:
cos(4θ) + 4cos(2θ) ≡ 8cos^4(θ) - 3

Thanks in advance!

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asked by Autumn
  1. cos(4θ) = 2cos^2(2θ)-1 = 2(2cos^2(θ)-1)^2-1
    4cos(2θ) = 4(2cos^2(θ)-1)
    so, add them up

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    posted by Steve

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