Ex 12.1, 6
An isosceles triangle has perimeter 30 cm and each of the equal sides is 12 cm. Find the area of the triangle.
Area of triangle = (s(s a)(s b)(s c))
Here, s is the semi-perimeter,
and a, b, c are the sides of the triangle
Given triangle is isosceles
In isosceles triangle, two sides are equal
So, a = b = 12 cm
and Perimeter = 30 cm
Semi-Perimeter = s =Perimeter/2
s = 30/2
s = 15 cm
We need to find c
Perimeter = 30cm
a + b + c = 30 cm
12 cm+ 12 cm + c = 30 cm
24 + c = 30
c = 30 24
c = 6 cm
Area of triangle = ( ( )( )( ))
Putting a = 12 cm, b =12 cm, c = 6 cm & s = 15 cm
= (15(15 12)(15 12)(15 6))
= (15(3)(3)(9))
= (15 (9)(9))
= ("9" 9) 15
= ("92" ) 15
= (9) 15
= 9 15
Thus, Area = 9 15 cm2

Made by

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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