In a triangle, the sum of two sides must be greater than the third side, and the difference between the two sides must be less than the third side, so the first question, the 6cm one must be the bottom, and the two sides are isosceles 12+ 12+6=30.

The second question, there are two cases, 8cm as the base, then isosceles 12cm, perimeter 12+ 12+8=32, another case, 12cm as the base, isosceles 8cm, perimeter 8+8+/kloc.