Cos ( 2x ) = cos ^ 2 (x ) sin ^ 2 (x ) = 2 cos ^ 2 (x ) 1 = 1 2 sin ^ 2 (x ) tan( 2x ) = 2 tan(x) / (1 tan ^ 2 (x )) Click to see full answerTan 2x ≠ 2 tan x by Shavana GonzalezThe fundamental identity states that for any angle θ, \theta, θ, cos 2 θ sin 2 θ = 1 \cos^2\theta\sin^2\theta=1 cos 2 θ sin 2 θ = 1 Pythagorean identities are useful in simplifying trigonometric expressions, especially in writing expressions as a function of either sin \sin sin or cos \cos cos , as in statements of the double angle formulas
Inverse Trigonometric Functions Wikipedia
