Take equal line segments on line segment AB (is it understandable? ), connect CD, make ∠ CDE = 30, and cross CB at point E. It can BE seen that Be increases with the increase of AD before point C, reaches the maximum when point E coincides with point C, and then gradually decreases. Or you can look at it by observing the graph, or take several maximum values, such as when CD is perpendicular to AB, when D is at the midpoint of AB, and so on.