Q. 12

# Find the value of 4cos^{3}30° – 3 cos30°.

Answer :

For θ = 30°,

4cos^{3}30° – 3 cos30° = 4cos^{3}θ– 3cosθ

We know that,

cos3θ = 4cos^{3}θ– 3cosθ

∴ 4cos^{3}30° – 3 cos30°

= cos(3 × 30° )

= cos90°

= 0

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