抛物线的焦点弦公式总结.ppt

21 22 xPBFxpAF pxy 22 pxy 2-2 21 -2-2 xPBFxpAF cos1cos1 pBFpAF cos-1cos1 pBFpAF PBFAF 211 . ),(),( 2211的倾斜角是直线的一条弦，设是抛物线过焦点已知AB yxByxAFAB 21 22 yPBFypAF sin1sin1 pBFpAF sin-1sin1 pBFpAF PBFAF 211 21 -2-2 yPBFypAF pyx 22 pyx 2-2 )( 21 xxpAB pxy 22 pxy 2-2 2sin2pAB )(- 21 xxpAB 2sin2 pAB )11(2 2kpAB )11(2 2kpAB pyx 2-2 )( 21 yypAB 2cos2 pAB )(- 21 yypAB 2cos2 pAB )1(2 2kpAB )1(2 2kpAB pyx 22 221221 4 pyypxx pxy 22 pxy 2-2 221221 4 pyypxx pyx 2-2 4 221221 pyypxx 4221221 pyypxx pyx 22 pxy 22 pxy 2-2 sin2 2PS OAB sin2 2PS OAB pyx 22 pyx 2-2 cos2 2PS OAB cos2 2PS OAB