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Cosine Rule

Triangles HOME | Achievement Criteria | Pythagoras | Trigonometry | Area | Sin Rule | Cosine Rule | Revision

8

Cosine Rule find a Side

Using the Cosine rule a2 = b2 + c2 - 2bcCos(A) to find an unknown side

Khan Academy Videos: Pythagoras Iintroduction & Example and problems to practice

MR notes, Blank notes

p435 Ex 31.01
p436 Ex 31.02

Youtube proof of Cosine rule

p139

Cosine rule to find a Side (java)

9

Cosine Rule find an Angle

Using the Cosine rule to find an unknown angle in a non-right angle triangle

MR notes, Blank notes

p439 Ex 31.03
p439 Ex 31.04

Youtube proof of Cosine rule

p140

Cosine rule to find an Angle (java)

10

Cosine Rule Applications

Using the Cosine rule to solve application problems involving finding sides or angles

MR notes, Blank notes

p442 Ex 31.05
p442 Ex 31.06

p141 & 142

 

Overview

The Cosine rule links THREE SIDES and ONE ANGLE in a triangle

Rule

Find Angles

Find Sides

Mouse over key words

Youtube proof of Cosine rule

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Find a Side

To find a side length in a triangle, given two angles and another side length.

Cosine rule to find a Side (java)

Rule

Find Side

Mouse over key words

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Find an Angle

To find an angle in a triangle, given two sides and another angle.

Cosine rule to find an Angle (java)

Rule

Working

Find Angle

Mouse over key words

Remember to inverse Cos-1

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Application

I sail from port on a bearing of 034 for 8km then south for 5km. How far back to port?

Draw triangle

Working

Solution

Mouse over key words

 

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