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

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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

by (128k points)
How it came here 1-2(2sin^2x cos^2x)^2
by (2.4k points)
Sorry i change my answer .......I make mistake....
by (128k points)
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