If both sides of an isosceles triangle are 3cm and 7cm in length, then its circumference is______  cm.

If both sides of an isosceles triangle are 3cm and 7cm in length, then its circumference is______  cm.

① When the waist is 3cm and the bottom edge is 7cm, it does not satisfy the trilateral relationship of the triangle, so it is discarded. ② when the bottom edge is 3cm and the waist length is 7cm, it can form a triangle, then its perimeter = 3 + 7 + 7 = 17cm