Trigonometric identities

A trigonometric identity is an identity that involves one or more trigonometric ratios.

$$tan\theta=\frac{sin\theta}{cos\theta}$$ $$sin^{2}\theta+cos^{2}\theta=1$$ $$sin(\frac{\pi}{2}-\theta)=cos\theta$$ $$cos(\frac{\pi}{2}-\theta)=sin\theta$$