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Homework Help: I am working though my maths courses

  1. Jun 28, 2013 #1
    using double angle formula and intergration.

    i was wanting to know why the the squared eitherside of the equals sign stayed the same.i thought square one side of the equals sign is root the otherside.

    this is some of my working.

    2 cos ^2_x-1= sin^2_x sin^2_x
    cos(2X)=Sin^2_x sin^2_x
    how does

    2√cosx=1/2 sin (2X)+c
    the answer is
    cos^2_x =1/4 sin (2x)+1/2x+c

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 28, 2013 #2


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    Why would you think that?

    2^2 = 2*2 = 4

    x^2 = x*x
  4. Jun 28, 2013 #3


    Staff: Mentor

    ??? What are you doing here?
    Also, don't connect equations with =. One equation is not "equal" to another.
    The line just above is wrong - it should be 1 - cos2/SUP](x) = sin2/SUP](x), but even so, how is it related to the line just above it?
  5. Jun 29, 2013 #4
    Anything you do to an equation you must do to both sides.

    If you square one side then you must square the other.

    As for your workings there is an error in the second line.
  6. Jul 8, 2013 #5
    you have said that everything you do to one side of the equals sign, you do to the other.what if you only want the a and not the a^2.what would you do to the equation.could you also tell me if you move -1 to the LHS of the equation will it be +1.Is there laws for the LHS and the RHS of equations.Like foils law or bodmass.
  7. Jul 8, 2013 #6


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    Gold Member

    Do you mean if you have ##a^2 = ...##, then how to get ## a = ...##? Consider this: If x = 7, say, then x2 = 49. How would you undo this operation?

    I wouldn't really call them laws, just mnemonics so as to remember how to multiply out binomials and order of operations when dealing with numbers.
  8. Jul 8, 2013 #7


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    To go from a^2 to a, you obviously have to take the square root. So if you have a^2 on one side of the equation (and NO other "a" in th equation) you take the square root of both sides of the equation.

    You don't "move -1 to the LHS". If you want to get ride of "-1" on one side of the equation you add 1 to both sides of the equation. -1+ 1= 0 so that will get rid of the -1.

    You talk as if these were totally arbitrary rules. The idea that -1+ 1= 0 is a basic fact of arithmetic. And the idea that if a= b then f(a)= f(b), for any function f, is a basic logical statement.
  9. Jul 12, 2013 #8
    If like the -1 you add 1 to both sides.would it be the same as or some thing like. x^2 and add ^-2 to both sides.
  10. Jul 12, 2013 #9


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    I have no idea what you could mean by "add ^-2". "^-2" is not a number (in fact, by itself if does not mean anything) and so cannot be "added". Do you understand what x^2 and x^-2 mean?
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