由题意 x 3 =-
b
k ,联立抛物线y=ax 2(a>0)与直线y=kx+b得ax 2-kx-b=0,∴ x 1 + x 2 =
k
a , x 1 x 2 =-
b
a ,∴
1
x 1 +
1
x 2 =-
k
b ,∴x 1x 2=x 1x 3+x 2x 3,
故选D.
由题意 x 3 =-
b
k ,联立抛物线y=ax 2(a>0)与直线y=kx+b得ax 2-kx-b=0,∴ x 1 + x 2 =
k
a , x 1 x 2 =-
b
a ,∴
1
x 1 +
1
x 2 =-
k
b ,∴x 1x 2=x 1x 3+x 2x 3,
故选D.