Question

using formula of cos3A, find the value of cos90°.... pls answer

Answer 1

you can write it as cos(3x30)
now apply formula, cos3A = -4cos^3A +3cosA

= -4(3√3 )/8 + 3√3 /2 [cos 30 = √3/2 ]
= -3√3/2 +3√3/2 =0.


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