First lets start with a triangle with sides a, b and c. Using the pythagorean theorem, we know that a2, b2 and c2:
Lets say that there is an angle x; between line b and line c. In that case, line a would be the opposite side, line b would be the adjacent side and line c would be the hypotenuse:
If we divide both sides by hypotenuse2, then:
Since cos(x) = adj/hyp and sin(x) = opp/hyp, then we can say that:
