Key Points - Heron’s Formula

1. Area of a Triangle – by Heron’s Formula
2. Application of Heron’s Formula in finding Areas of Quadrilaterals

- Heron's formula (sometimes called Hero's formula), named after Hero of Alexandria, gives the area of a triangle when the length of all three sides are known. Unlike other triangle area formulae, there is no need to calculate angles or other distances in the triangle first.

- Triangle with base 'b' and altitude 'h' is 
½ (b × h)

- Triangle with sides a. b and c = (a+b+c) / 2
( i ) Semi perimeter of triangle
( ii ) Area = sqrt [s(s − a)(s − b)(s − c) ]square units.

Equilateral triangle with side 'a'
 =sqrt (3)*a^2

Trapezium with parallel sides 'a' & 'b' and the distance between two parallel sides as 'h'.

Area = 1/2 * (a + b)h square units
 
- Rhombus with diagonals d1 and d 2
1 /2 * (d1 × d 2)

Perimeter = 2 * sqrt (d12 + d 22)