NCERT Solutions for Class 9 Maths Chapter 12
Important NCERT Questions
Heron’s Formula
NCERT Books for Session 2022-2023
CBSE Board, UP Board and Other state Boards
EXERCISE 12.1
Page No:203
Questions No:6
An isosceles triangle has perimeter 30 cm and each of the equal sides is 12 cm. Find the area of the triangle.
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Perimeter of triangle = 30 cm
Two sides of triangle b = 12 cm and c = 12 cm.
Let, the third side = a cm
We know that the Parimeter of triangle = a + b + c
⇒ 30 = a + 12 + 12
⇒ 30 – 24 = a
⇒ a = 6
So, the Semi- perimeter of triangle is given by
S = a + b + c /2 = 30/2 = 15 cm
Therefore, using Heron’s formula, the area of triangle = √s(s – a)(s – b)(s – c)
= √15(15 -6)(15 -12)(15 -12)
= √15(9)(3)(3)
= 9√15 cm²
Hence, the area of triangle is 9√15 cm².