xA=c,a=1,1=x²+y²/b²=c²+y²/b²=(1-b²)+y²/b²,yA=b².c+c=F1F2=3xBF1=3(-c-xB),xB=-5c/3.b²=yA-0=3(0-yB),yB=-b²/3.1=x²+y²/b²=xB²+yB²/b²=(-5c/3)²+(-b²/3)²/b²,9=25c²+b²=25(1-b²)+b²,b²=2/3，椭圆方程：x²+y²/(2/3)=1
用相关点代入法
