Can someone explain this to me? Please.

Discussion in 'Community Discussion' started by furious, Feb 27, 2007.

  1. furious macrumors 65816

    furious

    Joined:
    Aug 7, 2006
    Location:
    Australia
    #1
    How does 5 * (2 *a - 6*b^2) become 10 * a - 30 * b^2?

    I am doing revision as I have my first class of Quantitative Analysis for Business. All the maths I am fine with but Distributive Property of Multiplication. This is really making me nervous because getting a tutor through the Uni is impossible. I think it is something really simple if I could just find how this problem is solved. Thank you if you can help.

    ps Does anyone know of any web sites that might be of help. I have not looked yet.
     
  2. macdaddy121 macrumors 6502a

    Joined:
    Jan 8, 2003
    Location:
    Georgia
    #2
    I'm confused.....are you having trouble seeing that 5*2 is 10 and that 5*6 is 30....therefore 10a-30b^2? Is that what you are asking? You are just distributing the 5 through to the other two (2a & 6b^2).
     
  3. WildCowboy Administrator/Editor

    WildCowboy

    Staff Member

    Joined:
    Jan 20, 2005
    #3
    Have a look at this page to see if that helps explain things.

    When you have a sum (or a difference) in parentheses that is multiplied by something outside of the parentheses, the distributive property says that you can multiply each of the individual terms inside the parentheses by the multiplier.

    2(x+y) = 2x+2y
    2(x-y) = 2x-2y
     
  4. macdaddy121 macrumors 6502a

    Joined:
    Jan 8, 2003
    Location:
    Georgia
    #4
    I wish my test was on this tomorrow and not on linearization, differentials, and derivatives.....
     
  5. gauchogolfer macrumors 603

    gauchogolfer

    Joined:
    Jan 28, 2005
    Location:
    American Riviera
    #5
    Edit to avoid confusion: the stuff in bold should be 2a & 6b^2

    Everything else you wrote is fine.
     
  6. macdaddy121 macrumors 6502a

    Joined:
    Jan 8, 2003
    Location:
    Georgia
    #6
    oops....and that is where the silly mistakes come in.....-5 for me. :eek:

    Thanks.
     
  7. CanadaRAM macrumors G5

    CanadaRAM

    Joined:
    Oct 11, 2004
    Location:
    On the Left Coast - Victoria BC Canada
    #7
    Because the outside term has to be appied to each of the inside terms as separated by + or - operators

    5(a+b) = 5*a + 5*b

    Now, it doesn't matter particularly what the 5, the a and b are, as long as you apply the outside term to all of the insides.

    5*(2*a - 6*b^2) =
    (5*2*a) - (5*6*b^2) =
    (10*a) - (30*b^2)

    The tricky bit, which many people stumble on, is that if the outside term is a negative number, you have to carry through on the negative sign all the way through.

    -5 (a + b - c) =
    (-5*a) + (-5*b) - (-5*c) =
    -5a - 5b + 5c

    (as the two -'s make it +)
     
  8. furious thread starter macrumors 65816

    furious

    Joined:
    Aug 7, 2006
    Location:
    Australia
    #8
    Doh! I knew it would be so stupid as to make me blind.:eek: I have been on holidays for the last 4 months. I think I need a break. :p

    Wow! Can you be my teacher please. The Guy is a nut. I had him for Economics last year.

    Thanks for the web site. Looks to be really helpful. Very easy to understand the explanations.
     

Share This Page