Trigonometry

Radian - Definition, Formula, Conversion

A radian is the angle subtended at the centre of a circle by an arc whose length equals the radius. By definition, $\theta = s/r$ (arc length over radius). A full circle is $2\pi$ radians, so $360° = 2\pi$ rad, $180° = \pi$ rad, and $1\text{ rad} \approx 57.296°$.

Cos2x - Formula, Identity, Examples, Proof

The **cos2x identity** is the double-angle formula for cosine, with three equivalent forms: $$\cos 2x = \cos^2 x - \sin^2 x = 2\cos^2 x - 1 = 1 - 2\sin^2 x$$ The proof from the angle-sum identity, when to use each form, the related $\cos 2x$ in terms of $\tan x$, worked examples, and the most common student mistakes.

Trigonometry Formulas - Full list

The complete list of **trigonometry formulas** covers seven categories: basic ratios (sin, cos, tan), reciprocal identities (csc, sec, cot), Pythagorean identities ($\sin^2 + \cos^2 = 1$), angle-sum and angle-difference formulas, double-angle formulas, half-angle formulas, and sum-to-product formulas.

Sin Cos Tan - Trigonometric Ratios and Formulas

Trigonometric Table - Sin Cos Tan Values 0-90°

The trigonometric table gives the values of sine, cosine, tangent, cosecant, secant, and cotangent at the five standard angles: 0°, 30°, 45°, 60°, and 90°. The values come from two special right triangles - the 30-60-90 and the 45-45-90.