x^2-kx-（k+1）=0x1+x2=k,x1*x2=-(k+1) x1-x2=7 (x1-x2)^2=49 x1^2-2x1*x2+x2^2=49 (x1+x2)^2-4x1*x2=49k^2+4(k+1)=49k^2+4k-45=0 ...