Pythagorean theorem deals with right triangles and goes by the formula a^2+b^2=c^2. Sine, cosine, and the tangent of a triangle are used to find missing lengths and angles. Both theorems are used for this. However, the Pythagorean theorem is used to find only sides. The converse of sin, cos, and tan each go by the -1 power. These are used to find angles. Sin^-1*1 equals 90, cos^-1*1 equals 0, and tan^-1*-1 equals 45.
Did you at least know what the Pythagorean Theorem was before I told you this?