Question 257382
IF the perimeter = 20, then a side = 5.
using Pythagorean theorem, we get
 a^2 + b^2 = c^2
or
5^2 + 5^2 + c^2
25 + 25 = c^2
50 = c^2
c = sqrt(50) = 5sqrt(2).
This is the diagonal