Trigonometry in geometry

If the angle A is the right angle of the triangle ABC. The length of |AB|, |BC| and |CA| are usualy denoted by c, a and b. Take point B as center of a trigonometric circle (circle with radius = 1).

Now sin(B),cos(B) and 1 are proportional to b, c and a.

=> sin(B) = b/a
cos(B) = c/a
tan(B) = b/c
and because B + C = 90° =>
cos(C) = b/a
sin(C) = c/a
tan(C) = c/b