This problem needs to be discussed in categories: 1. When this triangle is an acute isosceles triangle, both waists are longer than the base. Take the midpoint of one waist and let this waist length be x, then the other waist length is 2x, 3x = 15, and x = 5, so the remaining waist length is 6,6-x = 6-5 = 65445. The foundation length is 1.

2. The bottom length is longer than both waists. Try to do the same as above, but 3x = 6, x = 2,15-x =15-2 = 13, so the base length is13.