trigonometric ratios

Sine, cosine, tangent, and their reciprocals, defined from a right triangle's sides.

For an acute angle $\theta$ in a right triangle with opposite side $o$ , adjacent side $a$ , and hypotenuse $h$ , the six trigonometric ratios are $\sin\theta=\frac{o}{h}$ , $\cos\theta=\frac{a}{h}$ , $\tan\theta=\frac{o}{a}$ , and their reciprocals $\csc\theta=\frac{h}{o}$ , $\sec\theta=\frac{h}{a}$ , $\cot\theta=\frac{a}{o}$ .