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SAI International School
CLASS - IX

Mathematics
CHAPTER-12: Heron’s Formula

Lesson Notes-1

SUB TOPIC: AREA OF TRIANGLE-BY HERON’S FORMULA

THINGS TO RECAP

 Rectangle

(a) Area = length  breadth
(b) Perimeter = 2 (length + breadth)
(c) Diagonal  (length  ) 2 (breadth
2
)
 Square
2
(a) Area = (side)
(b) Perimeter = 4  side
(c) Diagonal = 2 side
 Triangle with base (b) and altitude (h)

1

Area   b h
2
 Isosceles triangle, with base ‘a’ and equal sides ‘b’

Area of isosceles triangle  a 4b  2 a
2
4
 Equilateral triangle with side ‘a’

Area  3 a
2
4
 Parallelogram with base ‘b’ and altitude ‘h’

Area = b× h

 Rhombus with diagonals

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(a) Area  d  d
2 1 2
(b) Perimeter 2 d 2  d
2
1 2

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