You can find approximate sine values without a calculator by using the sine ratio. Sin A is equal to the length of the leg opposite of angle A divided by the length of the hypotenuse.

1. Find which trigonometric relationship you are using with SOHCAHTOA.
2. Take the inverse identity of your decimal, e.g., sin⁻¹(0.5).
3. The resulting number is the degree of your angle.
4. Check your results with our trigonometry calculators.

Trigonometry is the study of the relationships within a triangle. For right-angled triangles, the ratio between any two sides is always the same and is given as the trigonometry ratios, cos, sin, and tan. Trigonometry can also help find some missing triangular information, e.g., the sine rule.