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Homework Help: (r0q)(1)=? (q0r)(1)=?

  1. Nov 1, 2011 #1
    1. The problem statement, all variables and given/known data
    This problem is giving me issues, mainly because of how it is set up.

    2. Relevant equations
    Here is a picture of what my problem is,
    http://img23.imageshack.us/img23/1723/heko.png [Broken]

    3. The attempt at a solution
    I am attempting to solve this problem, and I haven't encountered anything like it in the book so far, I'm assuming I take the variables "q of x" and "r of x", but when solving, why are they swapped around? Is the (r0q)(1)= and (q0r)(1)= representing multiplication? I haven't seen that raised circle in the middle before. I'm assuming it has something to do with logarithms? I don't need anyone to show me how this particular problem is solved, [that would be cheating though it doesn't really matter to much in this class, 90% of the grade is based on the test]

    If someone could change the variables and numbers, and/or just go through the steps on how I should go about solving this type of problem, I would really appreciate it.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 1, 2011 #2
    Well this is the composition of functions, which is not commutative. That mean qor (using o as the symbol of composition for lack of a better button) does not necessarily equal roq.

    Do you know how to find q of r, ignoring the 1 for now?
  4. Nov 1, 2011 #3


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    The crucial point is, do you know the definition of "[itex]f\circ g(x)[/itex]"? This is known as the "composition of functions". If this is the first course in which you have seen it, I'll bet there's a definition in the same section of the book in which the problem occurs!
  5. Nov 1, 2011 #4
    Thank you for your help so far, because I now know it is a "Composition of functions" problem I was able to find out how to get started with this I think.
    r o q (1) can be re-written as (r(q(1)) from here, can I have a hint as to what the next step is?
    If the (1) were an x I would substitute in the variables and solve for x, however I'm not sure what to do with the (1)
  6. Nov 1, 2011 #5
    You can find q(1) first and then use that in r(x), or you can first find q of r as if you only had an x, and then substitute the 1 in the final step. Try both, you should get the same answer both times.
  7. Nov 1, 2011 #6
    Is there a special function you are talking about when you say find q(1) [in the first way to solve it you have posted] or are you just multiplying the q (x) variable times one?

    Sorry for my stupid questions, I have to figure this out somehow though!
  8. Nov 1, 2011 #7


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    To find q(1), substitute 1 in for the x that is given in the definition of q(x).

  9. Nov 16, 2011 #8
    edit: nevermind I found a forum with much more straightforward answers. Thanks anyway
  10. Nov 16, 2011 #9


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    Science Advisor

    Did you find a forum that will take your tests for you? Getting the answer to homework problems from others, rather than working them out for yourself is a sure way to fail a course.
  11. Nov 16, 2011 #10
    Actually I found a forum that instead of side tracking and telling me what I already know, actually showed me an example problem, and showed me the steps required to solve this type of problem. I learn in a different way than the community involved on this board apparently. Sorry if that offends you.
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