The laws of tangent (law of tan) describes the relation between difference and sum of sides of a right triangle and tangents of half of the difference and sum of corresponding angles. To understand the law of tangents for triangles and mollweide's equations. For a general triangle, which may or may not have a right angle, we will again need three pieces of information.

The law of tangents, also known as the tangent rule, states the relationship between the sum and difference of two sides of a triangle and the tangents of half the sum and difference of their opposite … Triangles and law of tangents. The law of tangents can be used to calculate the angles or sides of a triangle.