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Homework Help: Inverse func.

  1. Aug 1, 2011 #1
    1. The problem statement, all variables and given/known data

    y = 3

    2. Relevant equations

    3. The attempt at a solution

    Ive tried several times, I cant get the steps down. They say use reverse bedmass, and I dont understand.

    Here's what i did.

    y= 3/2(x-3)

    x= 3/2(y-3)

    x= 3/2y-6

    ___ = 3

    Which is already wrong, as you can see. Can someone please tell me the step so i can stop being stuck on this for 2 hours? =)
  2. jcsd
  3. Aug 1, 2011 #2
    "x= 3/2y-6"

    You were correct up to here. If it helps, write parenthesis in the denominator.


    What you did was just cancelled out the 6 in the denominator which you cannot do. Our objective is to get y by itself. Do that by multiplying 2y-6 to both sides. That should get rid of the fraction and leave you with.


    Try getting y by itself from here.
  4. Aug 1, 2011 #3

    x = 3 / (2y-6)

    x(2y-6) 3
    _______ = _____
    (2y-6) (2y-6)

    2xy-6x 3
    2y-6 2y-6

    Pretty sure im already wrong. .. .
  5. Aug 1, 2011 #4
    When I mean multiply both sides you don't do it like this:

    [itex]\frac{2y-6}{2y-6}[/itex] x=[itex]\frac{3}{2y-6}[/itex][itex]\frac{2y-6}{2y-6}[/itex]

    [itex]\uparrow\uparrow\uparrow\uparrow[/itex] That is a no no.

    You do it like this:


    Notice how the (2y-6) in the right side would cancel out. That would leave us with this.


    Remember this: If you do anything to one side, you MUST do it to the other side of the equation.
  6. Aug 1, 2011 #5
    So... the x still factors into 2y-6 on both sides..? your eq would give 2xy-6x/x on the left side..
  7. Aug 1, 2011 #6
    What do you mean "factors on both sides)? My equation would not leave you with a fraction (though the answer would be a fraction). Try distributing the x term to (2y-6). Then just solve for y.

    *Update: I see what you did. No that is wrong. Remember your algebraic properties:

  8. Aug 1, 2011 #7
    So, i did it like this..

    2x(y-3) = 3

    2x*y -6x =3

    2x*y = 6x+3

    y= 6x+3 /2x

    y= 3x +3/2x

    The answer is 2/3x +3 , however. Why is the x on the bottom?
  9. Aug 1, 2011 #8
    Starting from here:
    "2xy = 6x+3"

    We would divide 2x to get y by itself.


    I see you split the fraction on the right side to divide 6x/2x, however you forgot to cancel out the x. However you cannot divide 3/(2x), so that is why 2x is in the denominator. The answer would look like this.


    I do not see how the right answer is: "2/3x +3" (assuming this is (2/(3x))+3) the 3 is supposed to be in the numerator and 2x is supposed to be in the denominator.
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