Tangent half-angle formula

In trigonometry, tangent half-angle formulas relate the tangent of half of an angle to trigonometric functions of the entire angle. == Formulae == The tangent of half an angle is the stereographic projection of the circle through the point at angle π {\textstyle \pi } radians onto the line through the angles ± π 2 {\textstyle \pm {\frac {\pi }{2}}} .

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