An oblique triangle has no right angles. Yet trigonometry—a subject whose rules are generally based on right triangles—can still be used to solve a non-right triangle. However to do so you need some different variations of trigonometry- the laws of sines and cosines.

In an oblique triangle, there are six unknowns: the three angle measures and the three side lengths. To solve an oblique triangle you need one of the following sets of information as a given in any problem. They are as follows:

Two sides and an angle opposite one of the known sides (SSA)
Two angles and any side (SAA)
Two sides and their included angle (SAS)
All three sides (SSS)

One variation is where the given are side-side-side (SSS) as illustrated below.

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See also: Law of Cosines, Side-Angle-Side (SAS) and Law of Sines – Definitions for Surveyors