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Fairly basic algebra help?

  1. Feb 17, 2012 #1
    Hi, I'm having some trouble understanding how to tackle this question, I would appreciate it if some one could enlighten me on how to do this step by step and as in depth as possible.
    It may seem simple to some, but I am fairly new to this sort of equation.

    The equation is:
    −5[−2(m − 3n) + 4n]

    Josh, 13.
  2. jcsd
  3. Feb 17, 2012 #2
    You want to get rid of the brackets, basically, remember the order of operations (BODMAS) - here's a refresher:


    Just to get you started, let's do the first step:

    -5[((-2 * m) + (-2 * -3n)) + 4n]

    now, you should perform the multiplications inside the two inner brackets, which will leave you with -5[terms from expanded brackets], and you must multiply everything in those brackets by the -5
  4. Feb 17, 2012 #3


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    Ottahhh, we aren't allowed to just hand you the answer, but we can guide you step by step.

    Oh, and −5[−2(m − 3n) + 4n] is not an equation. What you have there is an expression. An equation is "expression = expression".
  5. Feb 17, 2012 #4


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    another way of thinking about BODMAS/PEDMAS is "inside-out":

    we want to get the "innermost" parentheses to go away first:

    -5[-2(m - 3n) + 4n]

    = -5[(-2)(m) - (-2)(n) + 4n]

    which is a consequence of the distributive law

    (the distributive law is your friend, give it some love).

    to take the next step, you have to use "the rules of sign":

    (-a)(-b) = ab
    (-a)(b) = -ab
    (a)(-b) = -ab
    (a)(b) = ab

    (sometimes recited as a chant:

    "positive times positive is positive, positive times negative is negative, negative times positive is negative, negative times negative is positive"

    ok, now just the people on the right:)
  6. Feb 17, 2012 #5
    Okay, so after all your help, I think I have an answer.

    How I got my answer:
    I started by focusing on the middle, we have -2 (m-3n) + 4n, I'm going to go
    -2 x - 3n, as deveno pointed out, 2 negative make a positive so -2 x - 3n = 6n, I'm then going to do -2 x m which will give me -2m so after them sums I have -2 (m + 3n) = -2m + 6n. I can't forget about the 4n so I must do [-2m + 6n + 4n] = [-2m + 10n]. I will then handle the -5, First off I must do -5 x -2m, 2 negatives give me a positive so I will get 10m as my answer. I must then do -5 x 10n which gives me -50n so after those 2 sums, I have -5[-2m + 10n] = 10m - 50n.
    Therefore my answer is 10m - 50n, please inform me of If I have gone wrong somewhere along the lines and consequently my answer is wrong.

  7. Feb 17, 2012 #6
  8. Feb 17, 2012 #7
    This isn't homework :p This is me having a genuine interest in learning new Mathematical methods.
  9. Feb 17, 2012 #8
    Yes, but it doesn't really matter if it's homework or not. You're trying to solve math exercises, and such things always belong in the homework forum here.
  10. Feb 18, 2012 #9
    As you wish (:
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