Question

An isoseles triangle has two sides of equal length. The third side is 5 less than twice the length of one of the other sides. If the perimeter of the triangle is 23 cm, what is the length of the third side? Explain how you would define a variable for this problem.

Answer 1

The length of third side is 9 cm.

Explanation:

Let,

x be the length of one side

Perimeter = 23 cm

Length of third side = 2x-5

Perimeter of isosceles triangle = 2a + b

23 = 2x + (2x-5)

23 = 2x + 2x - 5

23 = 4x - 5

23 + 5 = 4x

28 = 4x

4x = 28

Dividing both sides by 4

`(4x)/(4)=(28)/(4)\\x=7`

Length of third side = 2(7) - 5

Length of third side = 14 - 5

Length of third side = 9 cm

Hence,

The length of third side is 9 cm.