. Write the formula of Double angle
Double angle formulas are that formula which is used to express the trigonometric ratios of double angles (2θ) in terms of trigonometric ratios of single angle (θ). The double angle formulas are the unique cases of (and hence are derived from) the sum formulas of trigonometry and some alternative formulas are derived by the use of the Pythagorean formulas. Let us recall the sum formulas of trigonometry.
Double angle formula of sin, cos and tan are
-sin (A + B) = sin A cos B + cos A sin B
-cos (A + B) = cos A cos B - sin A sin B
-tan (A + B) = (tan A + tan B) / (1 - tan A tan B)