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Prove that cos 4x = 1 – 8sin^2 x cos^2 x

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+2 votes
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asked Aug 9, 2017 in Mathematics by sforrest072 (157,439 points) ● 61 ● 411 ● 949

Prove that cos 4x = 1 – 8sin2 x cos2 x

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+2 votes
answered Aug 10, 2017 by Ranjit (3,065 points) ● 8 ● 30
selected Aug 10, 2017 by sforrest072
 
Best answer

L.H.S=COS4x

R.H.L=1-8sin2x cos2x

         =1-2(2sinx cosx)2

         =1-2sin22x

         =cos4x.         (1-2sin2x=cos2x)

      L.H.L=R.H.L

commented Aug 10, 2017 by sforrest072 (157,439 points) ● 61 ● 411 ● 949
How it came here 1-2(2sin^2x cos^2x)^2
commented Aug 10, 2017 by Ranjit (3,065 points) ● 8 ● 30
Sorry i change my answer .......I make mistake....
commented Aug 10, 2017 by sforrest072 (157,439 points) ● 61 ● 411 ● 949
Thank you for helping
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