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Homework Help: A equation that im stuck on

  1. Feb 12, 2007 #1
    1. The problem statement, all variables and given/known data

    MathsQ1.jpg


    2. Relevant equations

    As in the image above

    3. The attempt at a solution

    I had a go but i rubbed it off the sheet.

    Can someone take me through this step by step on how to solve it

    Thanks
     
  2. jcsd
  3. Feb 12, 2007 #2

    HallsofIvy

    User Avatar
    Science Advisor

    What is your question? You are told exactly what to do!

    You are told that the equation must be of the form
    S= at2+ bt+ c.

    You are given t and S values for 6 different values of t.
    Putting the given x and t values into the equation above for 3 different values of t (t= 0, 2, 3, as they suggest, will do but the choice is yours) will give you 3 equations to solve for a, b, and c. (Taking t= 0 will get an especially easy equation!)
     
  4. Feb 12, 2007 #3
    so

    t=0: 0 = 0 + 0 + 0 (c will have to be 0 if a and b are)
    t=1: 10 =a+b+c
    t=2: 30 =4a+2b+c
    is that right?
     
    Last edited: Feb 12, 2007
  5. Feb 12, 2007 #4
    but where does it say a and b are 0?

    t=0: 0 = a.0 + b.0 +c and hence c=0

    the other equations are correct
     
  6. Feb 12, 2007 #5
    if t = 0
    then a x t = 0
    b x t = 0
    so c must be 0 if the equation equals 0
     
  7. Feb 12, 2007 #6
    Correct. Now use that you know c=0 in the other two equations
     
  8. Feb 12, 2007 #7
    Huh? I thought the other 2 equations were right?

    t=0: 0 = 0a + 0b + 0
    t=1: 10 =a+b+c
    t=2: 30 =4a+2b+c

    cant I right them as that?
     
  9. Feb 12, 2007 #8
    Yes they are correct but you now know that c = 0

    so a+b+c=a+b

    and

    4a+2b+c=4a + 2b
     
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