An oblique triangle is a triangle that contains no right angles. Oblique triangles are not as easy to solve as right triangles because three parts of the triangle must be known in order to solve the triangle. Also, with oblique triangles, we can no longer use two of the simplest techniques for solving right triangles--the Pythagorean Theorem and the fact that two acute angles are complementary. Instead, two new techniques are needed: the Law of Sines and the Law of Cosines. These laws are formulas that relate the parts of triangles to each other. They work for all triangles, including right triangles, but since right triangles have special properties we use simpler methods to solve them.
In the following lessons, we'll review oblique triangles and learn the Law of Sines and the Law of Cosines. In addition to that, we'll also see a new way to find the area of a triangle.