TrigonometryTrigonometric Identities

Trigonometric Identities cheat sheet

8 trigonometry formulas on one page. Print it or save it as a PDF from the print dialog.

Pythagorean

\sin^2\theta + \cos^2\theta = 1

Pythagorean (tangent)

1 + \tan^2\theta = \sec^2\theta

Double angle (sine)

\sin 2\theta = 2\sin\theta\cos\theta

Double angle (cosine)

\cos 2\theta = \cos^2\theta - \sin^2\theta

Sum (sine)

\sin(a \pm b) = \sin a\cos b \pm \cos a\sin b

Sum (cosine)

\cos(a \pm b) = \cos a\cos b \mp \sin a\sin b

Law of sines

\frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}

Law of cosines

c^2 = a^2 + b^2 - 2ab\cos C

Put the formulas to work