过椭圆x∧2/9+y∧2=1的左焦点F作弦ABF -2√2,0y=k(x+2√2)联立方程x^2/9+k^2(x+2√2)^2=1(k^2+1/9)x^2+4√2k^2x+2k^2-1=0由|AB|≤2 AB^2≤4设A：x1,y1B：x2,y2（y2-y1）^2+(x2-x1)^2≤4∵y1=k(x1+√2)y2=k(x2+√2)∴...