Area of a Triangle (OCR GCSE Maths)

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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

 

Examiner 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 degree3-3-2-area-rule-we-question

Calculate the area of triangle .

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

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Amber

Author: Amber

Expertise: Maths

Amber gained a first class degree in Mathematics & Meteorology from the University of Reading before training to become a teacher. She is passionate about teaching, having spent 8 years teaching GCSE and A Level Mathematics both in the UK and internationally. Amber loves creating bright and informative resources to help students reach their potential.