# Double angle formula proof tan

Jan 19, 2009 · Trig Tangent Double Angle Proof? I am trying to figure out how to prove the double angle formula for tangent(2a), but what I am looking at online has me a little confused. I know that tan(2a) can be separated into tan(a+a), but after that, what do I do? Jan 19, 2009 · Trig Tangent Double Angle Proof? I am trying to figure out how to prove the double angle formula for tangent(2a), but what I am looking at online has me a little confused. I know that tan(2a) can be separated into tan(a+a), but after that, what do I do? The formula of the tangent of the triple angle can also be proved by the following method. Let us consider the tangent of a sum: Deriving the tangent of a triple angle will require the formula of the tangent of a double angle: The cosine double angle formula tells us that cos(2θ) is always equal to cos²θ-sin²θ. For example, cos(60) is equal to cos²(30)-sin²(30). We can use this identity to rewrite expressions or solve problems. Learn mathematics online from basics to very advanced level with proofs of formulas, math video tutorials and maths practice problems with solutions.