Right triangles

In a right triangle, the sine of an acute angle is the length of the opposite side divided by the hypotenuse: $\sin \theta =\frac{\text{opposite}}{\text{hypotenuse}}$. The cosine is the adjacent side divided by the hypotenuse: $\cos \theta =\frac{\text{adjacent}}{\text{hypotenuse}}$. The tangent is the opposite side divided by the adjacent side: $\tan \theta =\frac{\text{opposite}}{\text{adjacent}}$. For any acute angle $\theta$, these ratios are fixed, so knowing one angle and one side lets you find any other side. The side opposite the right angle is always the hypotenuse; relative to $\theta$, the other leg is adjacent.