You can find by finding midpoint of the bottom two sides using midpoint formula which is (x+x1)/2, (y+y1)/2.
After that your answer will be something (x,y)
Then again you have to find midpoint, this time between top point and the midpoint of the two side which we just found. Imagine a straight line from top to the middle of the two side. Kind of like dividing triangle into two. After finding midpoint.
That's when you get centerfold of triangle.
