(15 marks) Suppose a ray comes from a point (2, 8) and hits at mirror point (6, 6). Assume that perpendicular vector a point (6, 6) is 𝑛̅= (0, 3). Find the reflection emitting point from (6, 6).

[Assume 2-D coordinate system, you must draw the appropriate diagram of your solution]

I'm pretty sure I can figure out the diagram, but I can't figure out what information I've been given and what is left for me to calculate. I can't draw a diagram that makes sense with what is being described. Does anyone know what I'm being asked here?

  • $\begingroup$ We require you to provide a reference to the source where you encountered this task: cs.stackexchange.com/help/referencing $\endgroup$
    – D.W.
    Commented Jan 31, 2023 at 21:31
  • $\begingroup$ We are a question-and-answer site. We require you to articulate a specific question in the body of your post. Also, we are not looking for posts that are just the statement of an exercise-style task. We are looking to build an archive of knowledge that will be useful to others. And, we expect you to show us your progress and your thoughts. We're happy to help you understand the concepts but just solving exercises for you is unlikely to achieve that. You might find this page helpful in improving your question. $\endgroup$
    – D.W.
    Commented Jan 31, 2023 at 21:32
  • 1
    $\begingroup$ @D.W., While I don't like the question much, it doesn't ask us to solve the exercise. While the post should specify what exactly is not clear in the statement, I myself don't know (and couldn't find) what "reflection emitting point" means, so the question "What is this question actually asking for me to solve?" sounds reasonable to me. Overall, I'm not sure the question should be closed. $\endgroup$
    – Dmitry
    Commented Jan 31, 2023 at 21:38
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    $\begingroup$ @Kaleb why not ask the teacher for clarification? $\endgroup$
    – Juho
    Commented Feb 1, 2023 at 5:38
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    $\begingroup$ I can't understand how to reconcile "I'm pretty sure I can figure out the diagram" and "I can't draw a diagram that makes sense with what is being described". $\endgroup$
    – D.W.
    Commented Feb 1, 2023 at 18:41

1 Answer 1


IMO the question is about a trick to handle reflections: rather than computing the direction of the incoming ray and deriving the direction of the outgoing ray, you can construct the symmetric of the emission point wrt the mirror. Then the reflected ray is the line from the reflected point through the hitting point.

enter image description here

  • $\begingroup$ Turns out the line through (0,3) and (6,6) was supposed to represent the mirror. Completely unclear from his wording though. Thanks for your help $\endgroup$
    – Kaleb
    Commented Feb 1, 2023 at 20:29
  • $\begingroup$ @Kaleb: no, the mirror is not through (0,3). $\endgroup$
    – user16034
    Commented Feb 1, 2023 at 20:47

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