# Cosine Rule – Finding Lengths

Students learn how to derive and apply the Cosine rule to find missing lengths in triangles.  As learning progresses they are challenged to apply multiple formulae involving triangles to solve more complex problems.
##### Differentiated Learning Objectives
• All students should be able to calculate an unknown length in a non right-angled triangle using the Cosine rule.
• Most students should be able to calculate a magnitude of direction using bearings and a length in a non right-angled triangle using the Cosine rule.
• Some students should be able to derive and apply the Cosine Rule to calculate unknown lengths in triangle shapes.

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