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Solving Triangles

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 180 .

A + B + C = 180

2.
The Sine Rule:



3. The Cosine Rule:

a
= b + c - 2bc cosA
or
b = a + c - 2ac cosB
or
c = b + a - 2ba cosC


Trig 3 PowerPoint File 0.6Mb




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