Their names and abbreviations are sine (sin), cosine (cos), tangent (tan), cotangent (cot), secant (sec), and cosecant (csc). There are six functions of an angle commonly used in trigonometry. trigonometry, the branch of mathematics concerned with specific functions of angles and their application to calculations. Trigonometry | Definition, Formulas, Ratios, & Identities. Covers Pythagorean Identities, verifying trigonometric identities, trig expressions, solving trigonometric equations, double-angle, half-angle, . Trigonometric Identities | Pythagorean Double Half Angle. If we combine those identities with other trigonometric identities, we have a powerful set of tools to help simplify expressions, factor expressions, and solve . Trig identitiesUsing Trigonometric Identities.