Huy137 Here is my problem: Those first two option is not good for animation so there should be some option which can change the angle of the polygon without changing the vertices's position. I hope we can upgrade this option into edit mesh menu soon:
Pharan Yes. Using the Create tool (the mouse cursor should have a + on it) in Edit Mesh mode, drag from one point to another point. It will result in an orange line, signifying that it's a user-defined edge rather than an auto-generated one.