1) Use the MIDPOINT

tool to plot the midpoints of any 2 sides of the given triangle.
2) Use the SEGMENT

tool to draw the segment (triangle midsegment) connecting these 2 points.
3) Use the SLOPE tool

to measure the slope of the midsegment and the slope of the side of the
triangle the midsegment doesn't touch. Then select the MOVE tool

. Drag
A, B, and
C around.