An isosceles triangle is said to have two equal sides and two equal internal angles. The perimeter of an isosceles can be found if the base and sides are known. 

Formula of Isosceles Triangle Perimeter

\[\large Perimeter\;of\;Isosceles\;Triangle,P=2\,a+b\]

Where,
a = length of the two equal sides
b = Base of the isosceles triangle

Solved Example

Question 1: What is the perimeter of an isosceles triangle when a = 9 cm and b = 6 cm?

Solution:

Given,
a = 9 cm
b = 6 cm

Perimeter of an isosceles triangle = 2a + b
= 2(9) + 6
= 18 + 6 cm
= 24 cm