Using the formula cos 2= 2 cos 2-1, find the value of cos 30, it is being given that cos 60=1/2
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Put A = 30°
2A = 60°
Cos A = √1 + cos2A / 2
Cos30° = 1 + cos60° / 2
= (1+1/2) / 2 = √3 / 2 /2
= √3 / √2 × 1 / √2 = √3 / 2
So, cos 30° = √3 / 2
2A = 60°
Cos A = √1 + cos2A / 2
Cos30° = 1 + cos60° / 2
= (1+1/2) / 2 = √3 / 2 /2
= √3 / √2 × 1 / √2 = √3 / 2
So, cos 30° = √3 / 2
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