(1) If the cardinal number is x, then the waist length is 2X, right? The sum of the three sides is equal to 18, so X+2X+2X= 18, then X=3.6, waist 7.2 and bottom 3.6.

(2) You don't necessarily think that if both sides are equal to 4, then the third side is equal to 18-4-4= 10, right? But there is a principle that the sum of any two sides must be greater than the length of the third side. Here 4+4=8 is not greater than 10.

But in another case, only one side is equal to 4, then the other two sides are 7, which conforms to the principle that the sum of any two sides must be greater than the length of the third side, so it is possible.