Formulas in Plane Trigonometry Formulas in Plane Trigonometry Log in to post comments Derivation of Basic Identities Derivation of Cosine Law Derivation of Pythagorean Identities Derivation of Pythagorean Theorem Derivation of Sine Law Derivation of Sum and Difference of Two Angles Derivation of the Double Angle Formulas Derivation of the Half Angle Formulas Book traversal links for Formulas in Plane Trigonometry Derivation of Heron's / Hero's Formula for Area of Triangle Up Derivation of Basic Identities