# Trig Identities

• The trigonometric identities are mathematical equations that relate the trigonometric functions (sin, cos, tan) to one another.
• There are many identities in trigonometry, but for revision, we are focusing on the primary ones: Pythagorean identities, Quotient identities, Co-Function identities, and Even-Odd identities.
• Pythagorean identities form the basis of trigonometry and are based on the Pythagorean theorem. These include `sin²θ + cos²θ = 1`, `tan²θ + 1 = sec²θ`, and `cot²θ + 1 = csc²θ`.
• Quotient identities express the functions in terms of each other. `tan(θ) = sin(θ)/cos(θ)` and `cot(θ) = cos(θ)/sin(θ)`.
• Co-Function identities describe the relationship between the sine and cosine of complementary angles. `sin(90° – θ) = cos(θ)` and `cos(90° – θ) = sin(θ)`
• Even-Odd identities pertain to the symmetry of the sin, cos, and tan functions. `sin(–θ) = -sin(θ)`, `cos(–θ) = cos(θ)`, and `tan(–θ) = -tan(θ)`.
• The key to mastering trig identities is practise. Work through several examples and apply each identity correctly.
• Remember, these identities will help later when solving trig equations or simplifying expressions.