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Basic Math Question

  1. Sep 10, 2004 #1
    How do I find a? there are two. y = a - ab
     
  2. jcsd
  3. Sep 10, 2004 #2

    Tide

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    a - ab is the same as a(1-b)
     
  4. Sep 11, 2004 #3
    simple ans............

    y = a - ab

    You have two a's on the right hand side (rhs). That's a problem.

    So we factor out the "a" on the rhs(right hand side). y=a(1-b).

    Now we only have one "a" on the rhs.

    a(1-b) means "a" multiplied by (1-b). To solve for "a" we must get rid of (1-b).We do the opposite of multiplying, which is????? yes yes yes dividing!

    Remember that what we do to one side we must do to the other.

    So we get y/(1-b) =a(1-b)/(1-b), (1-b) cancels on the rhs and we finally get

    y/(1-b) = a.

    :biggrin: :biggrin: :biggrin: :biggrin:
     
    Last edited: Sep 11, 2004
  5. Sep 11, 2004 #4
    factor
    please post in high school section next time about algerbra
    y = a - ab
    y= a(1-b) divide (1-b)
    y/(1-b) = a
     
  6. Sep 11, 2004 #5

    HallsofIvy

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    Don't get snippy, tom. There are some people (English majors?) who didn't take in math in high school (or didn't pay attention when they did) and are paying for it in college. If this was posted by a person who is in college, it belongs in this forum.
     
  7. Sep 11, 2004 #6
    My highschool algebra teacher would kill us if we ever divided by a variable. Its simply just bad algebra. While I agree that the only way to solve for a in this case is the way that was illustrated above, you should explicitly write for b not equal to 1.
     
  8. Sep 11, 2004 #7
    I'm 46 and decided to go back to college, they had me take this as a "refresher course" thanks for your help.
     
  9. Sep 11, 2004 #8
    whats wrong with dividing by variables?
     
  10. Sep 11, 2004 #9

    That's a very brave, usefull and rewarding decision Jason, I applaud you.

    I tutor students in their first years of mathematics and physics and I can tell you it ain't easy. Please, do not hesitate if you have any other question. I am willing to help you out if necessary. :wink: :wink:

    regards
    marlon
     
  11. Sep 11, 2004 #10

    You should never divide by a variable (well in 99% of the time) because you don't know what that variable is. You could be very well in fact be dividing by zero. For example x^2=2x. You can't divide both sides by x and get x=2. you have to subtract 2x from both sides and factor out the x and get your solutions as 2 and 0.
     
  12. Sep 11, 2004 #11

    HallsofIvy

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    You should never divide by a variable without specifying that the result is only true if the divisor is not 0. As gravenewworld said when asserting that you should not divide by 1-b, " While I agree that the only way to solve for a in this case is the way that was illustrated above, you should explicitly write for b not equal to 1."
     
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