a+b+c=2分之3倍根号2 (a+b+c)^2=9/2 a方+b方+c方=3/2 ab+ac+bc=(9/2-3/2)/2=3/2 所以 a方+b方+c方=ab+ac+bc=3/2 2a方+2b方+2c方=2ab+2ac+2bc=3 (a-b)^2+(b-c)^2+(a-c)^2=0 a=b=c 等边三角形