(a2+b2+c2)(1/b-1/c+1/c-1/a+1/a-1/b)= ___________________________________(a+b+c)(1/b-1/c+1/c-1/a+1/a-1/b)(a2+b2+c2)= ____________(a+b+c)(a+b+c)2= ____________(a+b+c)=1的平方=1