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This triangle has internal angles A, B and C, and sides of length a, b and c:

If three of these six measurements are known, then it may be possible to find the other three.

This is called 'solving' the triangle, and this topic will show you how to solve triangles for the unknown side and angles when any two sides and a non-included angle are given.

These are the formulas used to solve triangles:

1. The sum of the internal angles of a triangle equals 180º .

A + B + C = 180º

2. The Sine Rule:

3. The Cosine Rule:

a² = b² + c² - 2bc cosA

or

b² = a² + c² - 2ac cosB

or

c² = b² + a² - 2ba cosC

Trig 3 PowerPoint File 0.6Mb