Endee was asked to prove that any angle that forms a linear pair with a right angle must be a right angle. He drew the diagram shown here. Then he wrote the following 2-column proof. Which describes the error, if any, in Endee's proof?

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?