拋物線y^2=2px(p>0)上有A(x1,y1`),B(x2,y2),C(x3,y3)三點(diǎn)，F(xiàn)是它的焦點(diǎn)，若AF，BF，CF的長(zhǎng)成等差數(shù)列，則（ ）A。x1,x2,x3成等差數(shù)列 B.y1,y2,y3成等差數(shù)列 C.x1,x3,x2成等差數(shù)列D.y1,y3,y2成等差數(shù)列

熱心網(wǎng)友

選A。x1,x2,x3成等差數(shù)列 :拋物線上一點(diǎn)到焦點(diǎn)的距離，等于到準(zhǔn)線的距離：|AF| = x1 +p/2因此，若AF，BF，CF的長(zhǎng)成等差數(shù)列，則，2*BF = AF +CF即，2*(x2 +p/2)=(x1 +p/2)+(x3 +p/2)== 2*x2 = x1 +x3== x1,x2,x3成等差數(shù)列