设A(x1，y1)B(x2，y2)直线AB斜率为1，F1(-1，0)∴AB：y=x+1联立椭圆直线得7x²+8x-8=0x1+x2=-8/7，x1x2=-8/7|AB|=√[(x1-x2)²+(y1-y2)²]=√{(x1-x2)²+[(x1+1)-(x2+1)]²}=√[2(x1-x2)²]=√[2(x1+x2)²-8x1x2]=√[2×(-8/7)²-8×(-8/7)]=24/7
