... pp=- +22 4xxk hoc pp=++3 22 4xxkpp=+ 2 123 xk hoc pp=+3 2 4xk 0 ,25 2 i chiu iu kin ta cú 17 2, 2 121 2xkxkpppp=+=+ 0 ,25 ()() 2 33 2( )2( 1 )21 01 22 2 12 2ỡ++++-=ùớổử+=++-ùỗữốứợyxyyxxxyxyxx. ... iu kin: 1 2 x . 0 ,25 3 Ta cú: () 2 (1) 121 0 121 0(*)yxyx++-== < 0 ,25 www.VNMATH.com Thế vào (2) ta có: ()()( )3333 22 121 2xyxyxxxyxyxyÛ+=++-Û+=- 32 322 31 20 21 02( **) 2 xxxxxxyxyyyxyyyyæöæöæöÛ-++=Û-++=Û=-Û=-ç÷ç÷ç÷èøèøèø ... nờn: += 22 34ab 0 ,25 T ú ta cú h: 22 22 2 22 22 343 425 5,3,44 25 ()1695ababaabccababaỡ+=ỡỡ+==ùùùị===ớớớ=-==ùùợợùợ . Phng trỡnh chớnh tc ca elip l: 22 1 25 9xy+=. 0 ,25 7b...