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!

Embarrassingly easy algebra

  1. May 2, 2009 #1
    (please show how you rearrange the formula in blue i just need help showing me how you re arranged the question)

    two waves traveling reach the same destination
    wave 1 traveling at 8000m/s
    wave 2 traveling at 4500m/s
    wave 2 arrives 2 minutes after the first wave
    how far did they travel?


    v1=d/t1
    v2=d/(t1+120)

    t1 = d/8000

    4500 = d / ((d/8000)+120)

    every time i try solve for the awnser manually it's 274m (which is wrong)
    and i get the correct awnser from putting it in my graphics calculator and it's 1234285 meters (1.2*10^6 m)

    i have no idea how to re arrange it!

    4500 * ( (d/8000) + 120 ) = d
    4500 * (d/8000) = d-120
    4500 * d = (d-120) / (1/8000)
    i don't know
     
  2. jcsd
  3. May 2, 2009 #2
    Try distributing the 4500 first and then clearing the denominator :smile:
     
  4. May 2, 2009 #3

    Pengwuino

    User Avatar
    Gold Member

    On the 2nd to last step, you didn't distribute. Your 120 should be 120/4500 when it goes to the right hand side.
     
  5. May 3, 2009 #4
    Yeah guys i still don't understand, can you please give me the rule for dealing with
    4500((d/8000)+120) = d

    this is how i would solve it using what you've told me

    4500 ( d + 120 ) = d(8000)
    4500d + 4500(120) = d(8000)
    4500(120) = d(8000) - 4500(d)
    540,000 = 3500d
    540,000/3500 = d

    :\

    can you please show your step by step up to the awnser? (how ive shown it)
     
  6. May 3, 2009 #5

    Pengwuino

    User Avatar
    Gold Member

    You're not distributing before dividing by 8000.

    [tex]\begin{array}{l}
    4500((\frac{d}{{8000}}) + 120) = d \\
    \frac{{4500*d}}{{8000}} + 4500*120 = d \\
    \end{array}[/tex]

    You can work from there.
     
  7. May 3, 2009 #6
    how do i deal with the ds'?
    everytime i do something it gets cancelled or 8000d-4500d
     
  8. May 3, 2009 #7

    Pengwuino

    User Avatar
    Gold Member

    8000d - 4500d is simply 3500d
     
  9. May 3, 2009 #8
    yup, i know, it's just that 3500d = 4500*120
    540000/3500 = 154 which is wrong
     
  10. May 3, 2009 #9

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    You are still not "distributing" the 8000!

    From [tex] 4500((\frac{d}{{8000}}) + 120) = d [/tex]
    multiplying the equation by 8000, you get 4500d+ 4500*8000*120= 8000d or
    3500d= 4500*8000*120.
     
  11. May 3, 2009 #10
    what would this be called?
    distributing algebra? if you could tell me, ill google it and practise
    sorry for not really getting it i've never really dealed with this in physics or maths before
     
  12. May 3, 2009 #11

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    It's just the "distributive law"- surely you have done that before!

    Multiplying out the left side,
    [tex]\frac{4500d}{8000}+ 120*4500)= d[/itex]

    Now, multiply both sides of the equation by 8000:
    [tex]4500d+ 120*4500*8000= 8000d[tex]
    and, subtracting 4500d from both sides
    [tex]3500d= 120*4500*8000[/tex]
    It's that "8000" on the right side you are missing.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Embarrassingly easy algebra
  1. Easy Vector algebra (Replies: 5)

  2. Easy Algebra (Replies: 1)

  3. Easy algebra question. (Replies: 22)

  4. Easy algebra (Replies: 15)

Loading...