直线(m+1)x+(n+1)y-2=0与圆(x-1)^2+(y-1)^2=1相切，<==>|m+1+n+1-2|/√[(m+1)^2+(n+1)^2]=1,<==>|m+n|=√[(m+1)^2+(n+1)^2],平方得(m+n)^2=(m+1)^2+(n+1)^2,<==>2mn=2m+2n+2,<==>m+n=mn-1,?请检查题目
