Pythagorean Identity: This identity relates the three basic trigonometric functions (sine, cosine, and tangent) with the Pythagorean theorem.
Double Angle Identity: This identity allows us to express a trigonometric function of twice an angle in terms of the original angle.
Reciprocal Identity: This identity expresses a trigonometric function in terms of its reciprocal (e.g., cosecant is the reciprocal of sine).