Get the midpoints of AB and BC, using midpoint formula. So have those two new points.

Midpoint of (x1,y1) and (x2,y2) = ((x1+x2)/2,(y1+y2)/2).

Then get the distances of AC and the line segment connecting the two new points, using distance formula.

Distance between (x1,y1) and (x2,y2) = sqrt[(x2-x1)^2 +(y2-y1)^2].

You are asking only how to do it, so there.