The Cosine Law - Solving For Sides
This lesson works on a brand new equation. So far we have learnt how to solve for unknown sides only using the sine law. When solving for an unknown side the sine law requires the following:
- (ASA) Two angles and one side.
The problem with this is that we want to be able to solve problems that contains other sets of given information. Enter: The Cosine Law!
The cosine law allows us to solve for unknown sides of a triangle if given the following condition:
- Any two sides and a contained angle*
The important thing about building your cosine law equation is to make sure that the left side's side variable matches the angle's variable at the end. The following are three examples of how to build various equations for ∆ABC. The first is to find side a. The second is to find side d. The third is to find side c. It's important to notice how each unknown side in the equation matches to a known angle in the right side of the equation. Also how the other two sides each appear twice per equation.
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| The Cosine Law. Developed by Mike Studenny. |
The corresponding lesson to this blog post goes into detail on how to apply the cosine law to solve for an unknown side. The process for solving the equation is outlined there.
To view the video lesson follow the link below:
8.2 - Trigonometry - The Cosine Law - Solving for Sides
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