设a=x-y,b=y-z,-a-b=z-x(y-z)平方+(x-y)平方+(z-x)平方=(y+z-2x)平方+(z+x-2y)平方+(x+y-2z)平方b^2+a^2+(-a-b)^2=(-a-b-a)^2+(a-b)^2+(b+a+b)^2a^2+b^2+a^2+2ab+b^2=4a^2+4ab+b^2+a^2-2ab+b^2+4b^2+4ab+a^22a^2+2b^...