(1)x₁²/a²+y₁²/b²=1.........①
x₂²/a²+y₂²/b²=1............②
①-②,得
(x₁²-x₂²)/a²+(y₁²-y₂²)/b²=0.....③
(x₁+x₂)/2=-2/3
(y₁+y₂)/2=1/3
(y₁-y₂)/(x₁-x₂)=k=(1/3)/(-2/3+c)
分别代入③式,
2b²/a²=1/(3c-2)
而 c²=a²-b²,c²/a²=1-b²/a²
解得 a=2√2/3,b=2/3
椭圆方程:x²/(8/9)+y²/(4/9)²=1