With point d as DE⊥AB in e,

And DC⊥CB, AB⊥CB,

∴∠DEB=∠ABC=∠DCB=90，

∴ Quadrilateral DEBC is a rectangle,

In Rt△ADE, ∠ α = 43, DE = CB =139m.

As shown in fig. 3, point D moves on line segment OB (except endpoints O and B), and a straight line AB intersects with DE⊥CD at point E, that is, AB⊥x axis.