# Laws of Sines and Cosines

The laws of sines and cosines give you relationships between the lengths of the sides and the trig functions of the angles. These laws are used when you don’t have a right triangle — they work in any triangle. You determine which law to use based on what information you have. In general, the side *a* lies opposite angle *A*, the side *b* is opposite angle *B*, and side *c *is opposite angle *C*.