Cos^3 2a + 3 Cos 2a= 4 (Cos^6a - Sin^6a)
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Step-by-step explanation:
Pressumed that
4(cos6A - sin6A) = 4((cos2A)3 - (sin2A)3
= 4(cos2A - sin2A)(cos4A + cos2Asin2A + sin4A)
= 4(cos2A)(cos2A + sin2A)2 - sin2Acos2A
= 4cos2A(1 - sin2Acos2A)
= 4cos2A - 4cos2Asin2Acos2A
= 4cos2A - cos2Asin2(2A)
= 4cos2A - cos2A(1 - cos2(2A)
= 4cos2A - cos2A + cos3(2A)
= 3cos2A + cos3(2A)
= cos3(2A) + 3cos2A
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