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° = Cos90° = 0

RHS = 4Cos³ A - 3CosA = 4 Cos³30° - 3 Cos30°

= 4 × (√3/2)³ - 3×√3/2

= 4 × (3√3)/8 - 3√3/2

= 3√3/2 - 3√3/2 = 0

LHS = RHS

hence, proved

Answer 2

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