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Area of a Triangle

Maths: Edexcel A Level Pure Maths, topic 5.3.3

Area of a Triangle

We can use the formula: area of a triangle = 1⁄2ab sin(C).

Formula

Formula

  • Area of a triangle = 1⁄2ab sin(C) since the vertical height is b sin(C).
  • This formula can also be used to calculate the side length of a triangle whose area is known.
Example

Example

  • If we are given a triangle with two sides of 8cm and 10cm and the area is 20cm2, we can calculate the angle between the sides as follows:
  • 20 = 1⁄2 × 8 × 10 × sin(C)
  • 20 = 40 × sin(C)
  • sin(C) = 1⁄2
  • C = 30°

Test yourself on Area of a Triangle

  • Which is the correct formula for the area of a triangle?

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