Hello, johntuan!
Another approach . . .
Find the distance from A to the centroid of the triangle
with vertices: .
You are expected to know that the centroid is the common intersection of the medians.
Also, the centroid is the distance from a vertex to the midpoint of the opposite side.
The midpoint of side is: .
Distance is: .
. .
Therefore: .
Hi,
I've done this problem recently here:http://www.mathhelpforum.com/math-help/72933-post6.html