4.2 Non-right Triangle

Non-right triangles are triangles that do not have 90-degrees inside them. For this section, make sure you are across sine rule and cosine rule.

Sine Rule

The sine rule is useful as you can use it to find either a missing angle or length of an edge of triangle if you have enough information to use the sine rule equation.

Example 1

Consider the following triangles. Find x in each of the cases:

Cosine Rule

Consider the following situations:

All edges of the triangle are given but no angles are provided or two edges are given and the angle formed by them are given, and the third edge is to be calculated. In situations like these, the cosine rule is the quickest way to get to the answer.

Though there are three equations below, the basic idea is the same that you put the edges and angle enclosed by those edges on right side of equation and the edge opposite the angle on the left side.

Example 2

Consider the following triangles. Find x in each case:

There are broadly 2 types of questions you can expect in exam:

– 4.2.1 Exam Question Type 1

– 4.2.2 Exam Question Type 2

Study notes of this section and other resources can be accessed here:

– 4.2.3 Study Notes & Resources