Question

An isosceles 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 The third side is described in relation to one of the equal sides, so let x = the length of one of the equal sides.

Answer 1

The third side is described as 2x-5. The perimeter is the sum of the side lengths, so we have
  P = x + x + (2x-5) = 23
  4x = 28
  x = 7
The third side is 2·7 - 5 = 9 cm.