1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Solve for x

  1. Jan 17, 2005 #1
    For some reason i can't solve for x:

    0.012M/(d-x)^2=M/x^2

    I have M value: (5.98)(10)^24

    d is: (3.84)(10)^5
     
  2. jcsd
  3. Jan 17, 2005 #2
    show your work
     
  4. Jan 17, 2005 #3
    i started with cross multiplying:

    0.012Mx^2=M(d-x)^2

    0.012Mx^2=M(d^2-2dx+x^2)

    then i divided both sides by the left side and crossed out M.

    From there I don't know what to do
     
  5. Jan 17, 2005 #4

    BobG

    User Avatar
    Science Advisor
    Homework Helper

    After you divided both sides by M and then divided both sides by .012, you should have wound up with:

    [tex]x^2=\frac{d^2-2dx+x^2}{.012}[/tex]

    Split the right side up into three fractions:

    [tex]x^2=\frac{d^2}{.012}-\frac{2dx}{.012}+\frac{x^2}{.012}[/tex]

    Substitute in your value for d. That should leave you with something you can work with.
     
  6. Jan 18, 2005 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Actually, I wouldn't divide both sides by 0.012, just because I don't like fractions!

    0.012x2= d2- 2dx+ x2 is the same as (subtract 0.012x2 from both sides)
    0.988x2- 2dx+ d2= 0.

    With d= 3.85 x 105, d2= 1.48225 x 1011 so your equation is
    0.988x2- (7.7 x 105)x+ 1.48225 x 1011= 0.

    You can solve that with the quadratic formula.
     
  7. Jan 18, 2005 #6
    does d in this case stand for difference like in calculus or is it just any other variable?
     
  8. Jan 18, 2005 #7

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    By,the looks of it,it's a dimensionful number...

    Daniel.

    PS.Got it,it's the mean distance Earth-Moon and M is the Earth's mass... :tongue2: :approve: And it's in Km.
     
  9. Jan 18, 2005 #8
    couldnt you first divde M on both sides and then find the square root??

    as in

    [tex] \frac{0.012M}{(d-x)^2} = \frac{M}{x^2} [/tex]
    which then gives

    [tex] \frac{0.012}{(d-x)^2} = \frac{1}{x^2} [/tex]

    and then find the square rooton both sides

    [tex] \frac{\sqrt{0.012}}{d-x} = \frac{1}{x} [/tex]

    then cross multiply and solve without need for a quadratic??
     
  10. Jan 18, 2005 #9

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    I'm sorry,but it doesn't work that way.You need to consider the modulus when extracting sqrt,which would complicate the problem...

    Daniel.
     
  11. Jan 18, 2005 #10
    see i think it's this,
    0.012M/(d-x)^2=M/x^2

    cross multiply,

    x^2/(d-x)^2=M/0.012M

    x/(d-x)={1/0.012}^1/2 (that is sq root)

    x/(d-x)=9.13

    dividing the numerator & denominator by x

    1/{(d/x) - 1}=9.13

    {(d/x) - 1}=1/9.13
    =0.11

    (d/x)=1+.11
    =1.11

    since,d is: (3.84)(10)^5,we have

    x=d/1.11
    =(3.84)(10)^5/1.11
    =345,945.95 units
     
  12. Jan 18, 2005 #11

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    THAT IS DEVIOUS...U should have a [tex] \pm [/tex] sign... :grumpy:


    Daniel.
     
  13. Jan 18, 2005 #12
    if its correct please tell me. :smile:
     
  14. Jan 18, 2005 #13

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    I thought i put in a very obvious way... :tongue2: It's wrong.By inappropriately extracting square root,u lost one (possibly viable) solution.

    Daniel.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Solve for x
  1. Solve for x (Replies: 3)

  2. Solve For X (Replies: 5)

  3. Solve |x-1|e^x (Replies: 2)

  4. Solving for X (Replies: 5)

Loading...