Parallel or Not?

Part of the Congruence & Proof section of Coddy's Geometry journey. Lesson 45 of 63.

The parallel rules have one condition, and it is easy to forget: the lines must be stated parallel, by chevrons or in words. Two lines that only look parallel give you nothing, however carefully they were drawn.

$PQ parallel to RS with segments PS and QR crossing at O; the angles at Q and R are both 35 degrees$

With the chevrons, the 35° angle at Q fixes the alternate angle at R. Take the chevrons away and the angle at R could be anything, because the line RS could be tilted a little. So before you use a parallel rule, find the chevrons or the written given. If neither is there, the rule is not available.

Challenge

Segments AD and BC cross at M. The angle at A is 50°. Nothing says AB and CD are parallel. Is there enough information to find the angle marked ? at D? Choose Yes or No, then press Check.

Try it yourself

$Is there enough information?$