Q. 8 B5.0( 2 Votes )

If θ = 30°, verify that :

cos3θ = 4cos3θ – 3cosθ

Answer :

Given: θ =30o


Now, LHS = cos 3(30o)


cos 90o


= 0


Now, RHS = 4 cos3 θ - 3 cos θ


4 cos3 (30o) - 3 cos (30o)




= 0


LHS = RHS


Hence Proved


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