cosAcos (60-A)cos (60+A)=1/4(4cos a-3)
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Step-by-step explanation:
cosAcos (60-A)cos (60+A)
//But Cos (A+B) * Cos(A-B) = Cos²B - Sin²A
=> CosA(Cos²A - Sin²(60))
=> CosA( Cos²A - 3/4)
=> 1/4 [(4Cos³A - 3CosA)]
//But 4Cos³A - 3CosA = Cos3A
=> 1/4 [Cos3A]
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