Very good analysis and explanation guys! Let's go back to the topic, I heard about integral here, that's correct. I believe this is where the CG formula came from after evaluation. BTW for linear, graphical also works very well. For variable rates or curves, it is complex and can be solved accurately by integral.

If I'm not mistaken, MAC is defined by the product of square of chord and the half span of the wing divided by its (half wing) area. In other words it's the volume of a half wing panel divided by its area.