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Grr...Algebra

Discussion in 'Chit Chat' started by TyraBanksIsFierce, Nov 21, 2008.

  1. TyraBanksIsFierce

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    I have a test for all this stuff on tuesday, ive got most of it down except theres a few things i cant work out, like this problem:

    [​IMG]

    This ones a linear equation,

    you have to find out what X is

    i always end up with 1.25 but the answer is 6.25..

    I did a similar question and got it right, except it was more straightforward with no brackets and addition instead of subratction

    Can you help:icon_sad:
    Thankss

    Discuss
    -Algebra
    -Exams
    This Problem​
     
  2. Ok, so first you want to get a common denominator to subtract fractions. so multiply the top and bottom of the first fraction by 3/3 and the top and bottom of the second fraction by 2/2. So you get (6x-9/6)-(10x-10/6)=-4. Subtract the numerators to get -4x+1/6=-4. Multiply both sides by 6 to clear the fraction. So now you have -4x+1=-24. Subtract 1 from both sides and you get -4x=-25. Divide by 4 to get x=-25/-4. The negatives cancel and you get 25/4 which is 6.25.
     
  3. ArcusPuer

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    i dont see how it is 6.25
    i got 1.25 as well.
    perhaps the answer is wrong........?
     
  4. ArcusPuer

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    wait how did u get the +1?
    isn't it -9-10.... which is -19....
     
  5. Owen

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    [​IMG]

    It comes down to simplification. I'd start by multiplying that five on the top of the second fraction through what's in the parenthases.

    (2x-3)/2 - (5x-5)/3 = -4

    I'd then turn the whole left side of the equation into one fraction by multiplying the first fraction by 3/3 and the second fraction by 2/2. That way, you are effectively multiplying each fraction by one, which does not change the equation at all.

    (3/3)•(2x-3)/2 - (2/2)•(5x-5)/3 =-4
    (6x-9)/6 - (10x-10)/6 = -4

    We can now combine those two fractions into one fraction.

    ((6x-9) - (10x-10))/6 = -4
    (6x-9-10x+10)/6 = -4
    (-4x+1)/6 = -4

    We now multiply both sides by six to get rid of the fraction

    -4x+1 = -24

    We no subtract one from both sides...

    -4x = -25

    And divide both sides by -4.

    x = -25/-4 = 6.25

    Here's the math all together so it looks like work you would do on a homework assignment.

    (2x-3)/2 - 5(x-1)/3 = -4
    (2x-3)/2 - (5x-5)/3 = -4
    (3/3)•(2x-3)/2 - (2/2)•(5x-5)/3 =-4
    (6x-9)/6 - (10x-10)/6 = -4
    ((6x-9) - (10x-10))/6 = -4
    (6x-9-10x+10)/6 = -4
    (-4x+1)/6 = -4
    -4x+1 = -24
    -4x = -25
    x = -25/-4 = 6.25

    Edit: Damn! Beaten to it.
     
  6. Distribute the negative sign. It's -9--10. Two negatives make a positive.
     
  7. TyraBanksIsFierce

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    wow, i know what I did wrong now, I got -19 out of the -9 minus the -10

    forgot that negative a negative means is adding.

    Thank You!!
     
  8. TyraBanksIsFierce

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    Oh and thanks to anyone else who tried!
     
  9. Owen

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    When you subtract a negative number, you add it's possitive version, so if you subtract -10, you are adding 10.
     
  10. Owen

    In Loving Memory Full Member

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    Argh! Beaten again. :dry:
     
  11. ArcusPuer

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    ok i get it know, i forgot that u had to multiply the second fraction by the negative.
     
  12. starfish

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    Can you show us your solution so we can see where you went wrong.

    I worked it out and got x = 6.25


    Here is my solution.
    [​IMG]
     
  13. sdc91

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    The first step you should do is multiply everything by 6 to get rid of the fractions... starfish's solution works, but it makes it waaaaaaaaay easier to make mistakes.
     
  14. Amy

    Amy
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    Algebra is evil.
     
  15. Apocalypte

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    If any of you want a fright, my thesis for my CS degree will be based around a computational problem in algebra.
    Oddly enough, I'm probably a better mathematician than programmer...