Let x = the length of the smaller sides and y = the length of the longer sides. Since it's a pentagon, there are five sides. We have two unknowns (x and y) so we need two equations:
The perimeter is 17:
17 = x + x + x + y + y = x+y + x+y + x
The sum of a long side and a short side is 7:
x + y = 7
Substitute 7 in place of x+y in teh first equation:
17 = x+y + x+y + x
17 = 7 + 7 + x
17 = 14 + x
Solve for x. Once you have x, use x + y = 7 to find y.
