A1(-5,0),A2(5,0)为椭圆的两个顶点,
∴a=5,
F1(-4,0)F2(4,0)为椭圆的两个焦点,
∴c=4,b^2=a^2-c^2=9,
∴椭圆方程是x^2/25+y^2/9=1.①
设K(k,0),0