设弦所在方程为y-1=k(x-1)将y=kx-k+1带入x^2+2y^2=4得（1+2k^2）x^2-4k(k-1)x+2k^2-4k-2=0所以x1+x2=(4k(k-1))/(1+2k^2)因为（1,1）为中点所以（x1+x2）/2=1解得k=-1/2(x1-x2)^2=(x1+x2)^2-4*x1*x2=8/3lx1-x2l=2√6/...