设一点是A(Xa,Ya)那么对称点是B(4-Xa,2-Ya)A、B都在椭圆上：Xa^2+2Ya^2=2c^2Xa^2-8Xa+16+Ya^2-4Ya+4=2c^2两式相减：8Xa+4Ya-20=0所以 2x+y-5=0就是AB所在直线把y=-2x+5代入椭圆方程：x^2+2(-2x+5)^2=2c^29x^2-40x+50...