Trigonometry - Simple Identities (Edexcel A-Level Mathematics): Flashcards

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

$1 + \tan^2 \theta = \sec^2 \theta$ and $\csc^2 \theta = 1 + \cot^2 \theta$

$\csc \theta = \frac{1}{\sin \theta}$

$\sec \theta = \frac{1}{\cos \theta}$

$\cot \theta = \frac{1}{\tan \theta}$

$\tan \theta = \frac{\sin \theta}{\cos \theta}$

$\sin(A \pm B) = \sin A \cos B \pm \cos A \sin B$

$\sin \frac{\theta}{2} = \pm \sqrt{\frac{1 - \cos \theta}{2}}$

$\cos(-\theta) = \cos(\theta)$ (cosine is even)

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