Let the common sides have length x, i.e, we have 2 sides measuring x
the third side would measure 2x - 3.
The perimeter = x + x + 2x - 3 = 4x - 3 = 17
so, 4x = 17 + 3 ,
4x = 20
x = 20/4 = 5m
Therefore, the three sides are 5m , 5m and 2( 5 )-3 = 10 - 3 = 7m