Area Of Triangle
If you fold a square piece of paper diagonally (from corner to corner) in half, it makes a triangle.
If you fold a rectangular piece of paper diagonally in half, it makes another triangle.
Therefore, the rule for the Area of a Rectangle and the Area of a Triangle are related.
| Area of Triangle = | B × H |
| 2 |
where
B is the base
H is the perpendicular height (at right angles to the base).
All 3 triangles above have the same base, the same perpendicular height and therefore, all 3 triangles have the same area.
Example - Painting a Roof Gable
In this diagram of a roof gable at the front of a house, what is the area to be painted? (Include the window so there's paint left over.)
Answer:
Area of triangle
= (B × H) ÷ 2
= 10 × 2.5
= 25 m2
Maths Fun - Heron's Formula
Though more complex, this is a useful rule in real life because we only need to know the lengths of the 3 sides of any shaped triangle to find the area.
The sides are called a, b, and c.
Heron's rule has 2 parts:
| S = | (a + b + c) |
| 2 |
Area of triangle = √S ( S – a) (S – b) (S – c)
What is the area of a triangular city park whose sides are 100 metres, 150 metres and 200 metres?
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