Lesson Plan: Finding the Area of a Triangle Using Trigonometry Mathematics

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to find the area of a triangle using the lengths of two sides and the sine of the included angle.


Students will be able to

  • derive and recall the formula 𝐴=12𝑎𝑏𝐶sin,
  • use the formula 𝐴=12𝑎𝑏𝐶sin to calculate the area of a triangle given two of its lengths and an included angle,
  • calculate unknown lengths or angle measures given the area of a triangle,
  • calculate areas of parallelograms and other compound shapes using the formula.


Students should already be familiar with

  • right triangle trigonometry.


Students will not cover

  • the law of sines,
  • the law of cosines.

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