Two sides of a triangle have the same length. the third side measures 2 m less than twice the common length. the perimeter of the triangle is 14 m. what are the lengths of the three sides?

To find the perimeter you would add all the sides of the triangle together.  Represent the length of each side using the information given.

1 side =  x
2 side = x
3 side = 2x - 2

Add these together and combine the like terms.

x + x + 2x -2; the bold parts are the like terms

4x - 2 represents the perimeter.