抛物线y=ax2与直线y=kx+b(k≠0)交于A,B两点,且此两点的横坐标分别为x1,x2,直线与x轴的交点的横坐标是x3,则恒有( ) A.x3=x1+x2 B.x1x2=x1x3+x2x3 C.x3+x1+x2=0 D.x1x2+x
问题描述:
抛物线y=ax2与直线y=kx+b(k≠0)交于A,B两点,且此两点的横坐标分别为x1,x2,直线与x轴的交点的横坐标是x3,则恒有( )
A. x3=x1+x2
B. x1x2=x1x3+x2x3
C. x3+x1+x2=0
D. x1x2+x1x3+x2x3=0
答
,
y=ax2
y=kx+b,k≠0
∴ax2=kx+b,整理得ax2-kx-b=0,
由题设条件知x1+x2=
,x1x2=−k a
,x3=−b a
.b k
∴x1x3+x2x3=(x1+x2)x3=
×(−k a
)=-b k
=x1x2.b a
故选B.