1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I would appreciate some help with my geometry homework

  1. Aug 7, 2014 #1
    2. A group of Japanese physicists works on a project where planar lines are in the form of solutions to equations
    a⋅x+b⋅y+c=0
    where a , b , and c are fixed reals satisfying a2+b2≠0 . They need to know formulae for the images of the line a⋅x+b⋅y+c=0 in the following cases:
    1. Under the translation by a vector B=[u,v] ,
    2. Under rotation about a point (x0,y0) by 180 degrees,
    3. Under rotation about a point (x0,y0) by 90 degrees.
    Please provide those formulae and a justification for them.

    I know for number 1, you basically just add the vector B.
    for 2 and 3 I do not know whether to use point slope form and just change the slope or if I need to change the coordinates to (-y,x) for 90 degree rotation and (-x,-y) for 180 degree rotation but those are for rotation about the origin and my problem does not state that. Does the slope for a 180 degree rotation go back to the same slope? I am really confused on which direction to take.
     
  2. jcsd
  3. Aug 7, 2014 #2

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    Homework questions should be posted in the homework forum. ;)
     
  4. Aug 7, 2014 #3
    Sorry! I'm new and I looked for that but couldn't find it!
     
  5. Aug 7, 2014 #4

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

  6. Aug 9, 2014 #5
    Why don't you use a combination of the things that you know. I think the point of the problem is that you know how to translate the line. Thus, you know how to move the point ##(x_0, y_0)## to ##(0,0)##. Next, you say that you know how to do rotation about the origin. You can apply that concept. Finally, you just have to translate ##(0,0)## back to ##(x_0, y_0)##.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: I would appreciate some help with my geometry homework
  1. I need some help (Replies: 3)

Loading...