We are now going to extend trigonometry beyond right angled triangles and use it to solve problems involving any triangle. 1.Sine Rule 2.Cosine Rule 3.Area.

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Presentation transcript:

We are now going to extend trigonometry beyond right angled triangles and use it to solve problems involving any triangle. 1.Sine Rule 2.Cosine Rule 3.Area of a triangle

Throughout we will use the common triangle notation of capital letters for the vertices and corresponding, lower case letters for the sides opposite these vertices.

A B C a b c Side a is opposite to vertex A, side b opposite vertex B and side c opposite vertex C.

The sine rule = = = = For unknown angles For unknown sides

We can use the sine rule when we are given: 1. Two sides and an angle opposite to one of the two sides. 2. One side and any two angles.

Remember Try to use the formula with the unknown at the top of the fraction. We can use the sine rule to find the size of an angle or the length of a side.

9 cm 4 cm R Q P 75  Example 1: Find the size of angle R

R = 25.4  = = =

12 cm y R Q P 75  Example 2: Find the size of PR 65 

= = x sin65 =

The cosine rule a 2 = b 2 + c 2 - 2bc cos A b 2 = a 2 + c 2 - 2ac cos B c 2 = a 2 + b 2 - 2ab cos C

These formulae can be rearranged to give: Cos A = Cos B = Cos C =

The cosine rule a 2 = b 2 + c 2 - 2bc cos A Cos A =