1.

If sin A = \(\frac{1}{2}\) then 4 cos3 A – 3 cos A is: (a) 1 (b) 0 (c) \(\frac{\sqrt{3}}{2}\)(d) \(\frac{1}{\sqrt{2}}\)

Answer»

(b) 0

Given sin A = \(\frac{1}{2}\)

sin A = sin 30°

∴ A = 30° 

[∵ 4 cos3 A – 3 cos A = cos 3A] 

= cos(3 x 30°) 

= cos 90° 

= 0



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