问题
选择题
设F为抛物线y2=2x的焦点,A、B、C为抛物线上三点,若F为△ABC的重心,则|
|
答案
设A(x1,y1),B(x2,y2),C(x3,y3)
抛物线y2=2x焦点坐标F(
,0),准线方程:x=-1 2
,1 2
∵点F(
,0)是△ABC重心,1 2
∴x1+x2+x3=
,y1+y2+y3=0,3 2
而|
|=x1-(-FA
)=x1+1 2
,1 2
|
|=x2-(-FB
)=x2+1 2
,1 2
|
|=x3-(-FC
)=x3+1 2
,1 2
∴|
|+|FA
|+|FB
|=x1+FC
+x2+1 2
+x3+1 2 1 2
=(x1+x2+x3)+
=3 2
+3 2
=3.3 2
故选:C.