### Double Angle Theorem – Identities, Proof, and Application

The double angle theorem is the result of finding what happens when the sum identities of sine, cosine, and tangent are applied to find the expressions for $sin (theta + theta)$, $cos (theta + theta)$, and $tan (theta + theta)$. The double angle theorem opens a wide range of applications involving trigonometric functions and identities. […]

### Pythagorean Identities – Formula, Derivation, and Applications

The Pythagorean identities are important trigonometric identities that allow us to simplify trigonometric expressions, derive other trigonometric identities, and solve equations. Understanding these identities is essential when building a strong foundation to master trigonometric concepts and learn more advanced math topics. The Pythagorean identities are derived from the Pythagorean theorem. We use these identities to […]

### Cosine Theorem – Explanation & Examples

The law of cosines or cosine theorem is a rule that provides us with the relation between the sides and angles of a triangle. The relationship is described using the formula: $c^2 = a^2 + b^2 -2abcos (z)$ or $c = sqrt{a^2 + b^2 -2abcos (z)}$, where $a$, $b$ and $c$ are the three sides […]