3a is the line segment AB, so that AB=2a, a _ _ _ _ _ _ _ _.

(1)3a+2b is to draw BC to the right with point B as the endpoint, so BC = 2ba _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

(2)3a-2b, that is, with point B as the endpoint, draw BD to the left, so that BD = 2bd _ _ _ _ _ _ A _ _ _ _ _ _ B.

Because it is not easy to operate, the bottom of point A is connected together.

(Description, when 3a & gt2b, D is on the right of A,

When 3a=2b, d coincides with a,

Dang3a