Notice that we have a case of two parallel lines intersected by a transverse line that forms with them acute and obtuse angles.
It is absolutely true that all acute angles formed are of the SAME measure, and that all obtuse angles formed are of the SAME measure.
And given that one obtuse angle plus an acute angle in the picture render a straight line, it is the same as saying that their addition renders 180 degrees.
It is TRUE that adding any obtuse angle plus any acute angle in the image provided will render 180 degrees.
