An irregular pentagon has vertices A,B,C,D,E, with the angle at B being re-entrant and of 270 degrees, and those at C,E being right angles. These lengths are given: AB=3, BC=4, CD=5, AE=4.

(Stop this video around 17 seconds in, and there is a diagram of the figure.) Construct line AC.

Prove that AC and DE are parallel.