Question 439037
Let x = length of one of the two congruent legs, and 
y = the base.
Then 2x+y = 12. 
From the triangle inequality, 2x > y ==> 2x > 12 - 2x
==> 4x > 12 ==> x > 3.
Hence the conditions that must be satisfied are y >0, x >3, and 2x + y = 12.
(for example, x = 7/2, y = 5, so that 2*x+y = 7 + 5 = 12.)