The Tangent is a Tangent! Out of the Math Box! - Debra Borkovitz
6 Feb 2012 In my post Trigonometry Yoga, I discussed how defining sine and cosine as lengths of segments in a unit circle helps The geometric definition of the tangent function, which predates the triangle definition, is the length of a segment tangent to the unit circle. and the line x=1, i.e. the tangent to the unit circle at B. Then tan ? 牟 is the y-coordinate of C, i.e. the signed length of segment BC.