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Cosine Rule 1

In the diagram above, traingle BCD is equilateral. AB = 3BC. BD is k units.
Determine the length of AD.

SOLUTION

We start by identifying and calculating angles.
B1 = 600
B2= 1800 - 600=1200

From Given
Given that BD = k units.
Then BC = k units as well (equilateral)
Then AB = 3k units.

Now use the cosine rule as follows:

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