Area of smaller circle when angle bisector divides 60° angle in cone

[athena810]

Homework Statement

A right circular cone is drawn above, with 2 circles centered at A on its base as shown. AB is the height of the cone, the measure of <ABC is 60° and BC has a length of y. If BD bisects <ABC, which one of the following gives the area of the smaller circle in terms of y?

http://imgur.com/JgrevjM

Homework Equations

none

The Attempt at a Solution

Included in the picture

Could you explain what I did wrong, and how to get the correct answer? Thanks

 

[gopher_p]

BD doesn't bisect AC.

 

[athena810]

Doesn't bisecting cause the bisecting thing to bisect the line segment from where the angles end?

 

[Office_Shredder]

It bisects the angle ABC, it does not cut the line AC in half (which seems to be what you are using)