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Homework Help: Y=sin2x +cos3x

  1. May 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Consider the function y=sin2x +cos3x

    A.] Find a value for y if x= pie radians.

    B.] Find y if x= 0.3 radians.

    C.] What is the period of this function? Show how you obtained your answer?

    3. The attempt at a solution

    What I would like to know is how would I go about doing this question.

    That is all.

    I am very fuzzy with doing any of this work, and would like to know how to best tackle the problem.

  2. jcsd
  3. May 26, 2010 #2


    Staff: Mentor

    First off, pie is a kind of dessert food, and pi is the name of the Greek letter.

    For the first two parts, do you know how to evaluate a function? That is all that is being asked in a and b.

    For the third part, you need to know the periods of sin(2x) and cos(3x), and then find the smallest value that both periods evenly divide.
  4. May 26, 2010 #3
    For A and B:
    Write out y but with the given value of x substituted in. You then just have to do the 'adding up'.
    For B you need a calculator. Do A with a calculator if you want, and see if you can use any facts you've learnt to figure out why it's such a simple number

    C is a bit trickier.
    Do you know what the period of a function is?
  5. May 26, 2010 #4
    I use to know but far to rusty. And don't have my old books to look at.

    So no don't remember the period of the function.

  6. May 26, 2010 #5


    Staff: Mentor

    This is exactly the same question you posted back in August of last year - https://www.physicsforums.com/showthread.php?t=332587. We have given you some advice on how to proceed on the first two parts, so have at it. For the third part you need to expend some effort (like getting a book or doing an internet search) to help yourself.
  7. May 26, 2010 #6


    User Avatar

    Staff: Mentor

    The period of a sine wave is just where the waveform repeats. So one period is one cycle of the sine wave:


    As stated, your previous thread would seem to have helped you to figure out the first 2 questions.

    In the 3rd part of this problem, you need to figure out where the 2 sinusoid waves cross the x-axis for the repeated pattern.
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