Area Of A Triangle

This lesson covers:

  1. How to find the area of a triangle using the formulas:
  2. Area = 12\frac{1}{2} x b x h
  3. Area = 12\frac{1}{2} x a x b x sin(c)
Diagram showing the area formulas for triangles, including base times height and half ab sine C.

Which formula would you use to calculate the area of the triangle below?

Right-angled triangle with base 5 cm and height 8 cm.
Area = length x width
Area= 21​× base x height
Area = 21​×a×b×sin(c)

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Right-angled triangle with sides labeled 10 cm and 7 cm.

Calculate the area of the triangle above.

(Shape not drawn accurately)

35

cm2

cm2

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Diagram showing a right-angled triangle with a height of 6 mm and a base of 14 mm.

Calculate the area of the triangle above.

(Shape not drawn accurately)

42

mm2

mm2

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Calculate the area of the triangle below.

(Shape not drawn accurately)

Diagram showing a triangle with a base of 20 cm and height of 12 cm.
120

cm2

cm2

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Calculate the area of the triangle below. 

(Shape not drawn accurately)

Triangle with a base of 4 cm and height of 3 cm used to calculate the area.
6

cm2

cm2

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Triangle with sides 20 meters and 17 meters, and a 30 degree angle.

Calculate the area of the triangle above. 

(Shape not drawn accurately)

85

m2

m2

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Triangle with sides 29 cm and 33 cm and an angle of 105 degrees.

Calculate the area of the triangle above. Give your answer to 3 significant figures.

(Shape not drawn accurately)

462

cm2

cm2

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Diagram of a triangle with sides labeled 28 m and 52 m, and angle x highlighted in green.

The area of the above triangle is 600 m2. Calculate angle x. Give your answer to 3 significant figures.

(Shape not drawn accurately)

55.5

°

°

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Diagram of a triangle with sides labeled 19 mm and 22 mm, and angle x to be calculated.

The area of the above triangle is 200 mm2. Calculate angle x. Give your answer to 3 significant figures.

(Shape not drawn accurately)

73.1

°

°

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