prove that cos^2 2x = 1/2(1 + cos 4x)
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Step-by-step explanation:
cos4x
= cos (2x + 2x)
= cos 2x cos 2x - sin 2x sin 2x
= cos²2x - sin²2x
= cos²2x - 1 + cos²2x
= 2cos²2x - 1
Thus cos²2x = ½ ( 1 + cos4x )
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