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Thread: Making X the subject

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    Post Making X the subject

    It seemed simple at first but I cant seem to make X the subject of this formula. :|
    a = (2x + 1) / (x + 2)

    I've managed to rearange it so that there is only one x:
    a = 2 + (5 / (x - 2))

    What do I do after that?

    The actual question was to find the equation of ƒ^-1(x) when ƒ(x) = a.

    ~
    I dont have access to a computer atm so refrain from posting attached files unless it in necessary ty =)

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    switch x and a then solve for x.

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    well you could use this website if you don't need the work
    http://www.wolframalpha.com/input/?i...28x%2B2%29%3Da
    they show it as the answer being:
    x = (1 - 2a) / ( a + 2)

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    Umm Im not sure what you mean by that... bolshak
    I need x in terms of "a" ... preferably with only one "a" term.

    Edit: thanls thisguy but i need to know how to work it out .. there seems to be no working out in this one
    Last edited by logical; 01-21-2012 at 05:05 PM.

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    Quote Originally Posted by logical View Post
    Umm Im not sure what you mean by that... bolshak
    I need x in terms of "a" ... preferably with only one "a" term.

    Edit: thanls thisguy but i need to know how to work it out .. there seems to be no working out in this one
    F^-1X = Inverse of F'(x)

    They're asking you for the inverse function..

    y = 1/x.. inverse would be x = 1/y.. When you swap a with x, just solve to isolate a again. that's it.
    I am Ggzz..
    Hackintosher

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    Quote Originally Posted by ggzz View Post
    F^-1X = Inverse of F'(x)

    They're asking you for the inverse function..

    y = 1/x.. inverse would be x = 1/y.. When you swap a with x, just solve to isolate a again. that's it.
    but the "2+" makes things more complicated than simply swapping the two:
    for x = 1/y
    multiply the equation by y
    xy = 1
    and divide by x
    y = 1/x

    however with x = 1/y + 1 :
    multiply by y
    xy = 1 + y
    divide by x
    y = (1 / x) + (y / x)
    y = (y + 1) / x
    ... it doesn't work as well.
    still stuck .. unless some1 posted in the age ot took tp type this on a 3ds ›.‹

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    Bleh I'm bored.
    a = (2x + 1) / (x + 2)
    a(x+2) = 2x+1 (multiply both sides by x+2 to get rid of the fraction)
    ax+2a = 2x+1 (get rid of brackets)
    ax=2x-2a+1 (substract 2a from both sides to get 2a to the other side)
    ax-2x = -2a+1 (substract 2x from both sides to move it to the left)
    x(a-2) = -2a+1 (everything on left side is multiple of x, so we take x out of brackets)
    x = (-2a+1)/(a-2) (divide both sides by a-2)

    For this kind of stuff (high school math I assume), this always works:
    Get rid of the fraction, by multiplying both sides by it (not by using long division, though that would work but it's ugly and requires work)
    Every term with X at one side (in this case left side), everything else right side
    Factor X out, so you get x(...) = ...
    Divide both sides by the term after X

    The above always works for this kind of excercises. The real trick is moving everything with X to one side and everything else to the other side.
    Last edited by Markus; 01-31-2012 at 03:36 PM. Reason: Fixed that error of 2 posts below, thanks!
    I made a new script, check it out!.

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    ah! silly me... done the division coz i learnt it recently and assumed that was what i was meant to do, misleading me :P
    Thats my excuse anyway .
    Ty Markus =D

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    Quote Originally Posted by Markus View Post
    ax=2x-2a+1 (substract 2a from both sides to get 2a to the other side)
    ax-2x = 2a+1 (substract 2x from both sides to move it to the left)
    Made a mistake here, you dropped the "-" in front of the 2a in the second line, would still get all the method marks though ;P

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