Question

. If ∠A = 30º, then show that cos3A = 4cos3A – 3cosA​

Answer 1

Step-by-step explanation:

Angle A = 30°

LHS= Cos 3A = Cos 3×30° = Cos 90° = 0

RHS 4 Cos A 3CosA 4 Cos 30° - 3 Cos30°

4 x (v3/2) - 3xv3/2

= 4 x (3v3)/8 - 3V3/2

= 3V3/2 - 3v3/2 = 0

LHS = RHS

hence, proved

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