Facts That Matter- Heron’s Formula | Mathematics (Maths) Class 9 PDF Download

• Area of a triangle
• Heron’s formula: For sides of a triangle being a, b, c, the semi-perimeter and area of the triangle =
• For finding the area of a quadrilateral, we divide it into various triangles. Then we use Heron’s formula to find the area of the triangles.

Area of Triangle

We have already learnt that area of a triangle
[altitude corresponding to that side (or height)]

 [altitude corresponding to base (or height)]

Thus, the area of a triangle

Note: 
Unit of measurement for area of any plane figure is taken as square metre (m²) or square centimetre (cm²), etc.

Heron's Formula

When it is not possible to find the height of the triangle easily and measures of all the three sides are known then we use Heron’s formula, which is given by
Area of a triangle =
where a, b and c are the sides of the triangle and s = semi-perimeter, i.e. half the perimeter of the triangle =

Area of an Equilateral Triangle

Let the side of the equilateral triangle be ‘a’.
∴
⇒ Area of the triangle

Thus, the area of an equilateral triangle