Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

2a x 2x = 4ax

  1. Jul 17, 2009 #1
    Hi All, this is not homework, just some basic revision for my own personal understanding, it's a long time since I went to school?

    I would like to refresh my mind on the following algebra please.

    4ax + 2ay = 2a x 2x + 2a x y
    = 2a(2x + y)

    Sorry for not using the DOT product as it does not seem to be available, so had to use X for multiplication?

    My misunderstanding of the above is, what happend to the 2a on the right hand side of the first line above?

    I understand that 4ax is made up of 2a x 2x = 4ax, and I understand that 2a(2x is made up of the 4ax, but i can't get my head round where the 2a went on the right hand side?:confused:

    any help greatly appreciated

  2. jcsd
  3. Jul 17, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Re: Algebra

    Let's review

    4ax+2ay this is your starting equation

    2a*2x + 2a*y this is the same equation, only we've split 4ax into 2a*2x and 2ay into 2a*y

    2a*(2x+y) you've factored 2a out of the equation. Recall distribution: b*(c+d) = b*c + b*d always. This works backwards just as well...b*c+b*d = b*(c+d) which is what's been done here with b=2a, c=2x, d=y

    So what's the sticky point?
  4. Jul 17, 2009 #3
    Re: Algebra

    Hi Office_Shredder. Please stick with the original equation as the "learner" that's "me" is trying to achieve the understanding of the idea of "Factorisation" from first principles, therefore if you expand with more ideas before I gain the basics, I will be lost:confused:

    Let's start with my original equation;

    4ax + 2ay = 2a * 2x + 2a * y (the astrict in my example means multiplication)
    =2a(2x + y) (if I now multiply this out I get)
    = 4ax +2ay
    Here is my problem:confused:

    2a * 2x = 4ax:smile: 2a * y = 2ay, but where did the "other" 2a appear from?

    am I right in thinking that the 2a on the left hand side of the equation has been moved to the right hand side, and the y placed inside the bracket?
    When I multiply them out the original equation can be found, which seems right, but my understanding is that "if a number on the left hand side of the equals is positive, then moving it to the right hand side should make it negative"?

    So; 4ax = 2a * 2x and 2ay = - 2a * y or is there different rules for different types of maths?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook