Hey rcs.
I'm in agreement with you: I have no idea what this actually means.
I would offer a speculation that it turns a triangle into a quadrilateral on the x-y plane.
In triangle ABC , is produced to D. If angle A is 60 and angle B is 85. Find angle BCD.
I would like to know what does it look like when it say produced to D. I dont understand the statement. I need your help please. Thanks a lot