在椭圆x^2/25+y^2/16=1上求一点,使它到右焦点的距离等于到左焦点距离的2倍

右焦点(3,0),左焦点(-3,0)设所求点是(m,n)(m-3)^2+n^2=4[(m+3)^2+n^2](m-3)^2-4(m+3)^2=3n^2(m-3+2m+6)(m-3-2m-6)=3n^2(m+1)(-m-9)=n^2代入椭圆m^2/25+(m+1)(-m-9)/16=19m^2+250m+625=0m=-25,m=-25/9m=-25,n无解m=-2...