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Area of a Triangle

Area of a Triangle

How do I find the area of a non-right triangle?

  • The area of any triangle can be found using the formula

A space equals space 1 half a b sin C

    • Where C is the angle between sides a and b
    • You need to remember it
  • Be careful to label your triangle correctly so that C is always the angle between the two sides
  • Sin 90° = 1 so if C = 90° this becomes Area = ½ × base × height
  • If you know the area you can use the formula to find the length of a side or the angle
    • Using inverse sin will always give you an acute angle
    • Subtract the value from 180 if you need the obtuse angle

Exam Tip

  • Remember to check that your calculator is in degrees mode!

Worked example

The following diagram shows triangle  ABC . AB space equals space 32 space cmAC space equals space 1.1 space straight m , B A with hat on top straight C space equals space 74 degree 3-3-2-area-rule-we-question

Calculate the area of triangle .

3-3-2-ai-sl-area-rule-we-solution

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