Commutative, Associative Property Question

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Gina
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Commutative, Associative Property Question

Postby Gina » Fri May 29, 2009 12:21 am

I hate being unsure about these things but I don't want to get in a habit of doing it wrong.

Here's an example:

9 + 2y + x - 25 + 3 + x

In using the commutative property, when I move stuff around, is there a rule as to which order it should be in? If I arbitrarily move things around I'll end up with different solutions, obviously.

So, if a constant comes first, a 'y' monomial second, and an 'x' variable third, should I move all the constants up, then the 'y' monomials, followed by the 'x' variables?

9 - 25 + 3 + 2y + x + x


According to PEMDAS, I should do addition before subtraction. So, the associative step would look like this:

9 - (25 + 3) + 2y + (x + x)


Or should I just go in order: (9 - 25) + 3 + 2y + (x + x)

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stapel_eliz
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Re: Commutative, Associative Property Question

Postby stapel_eliz » Fri May 29, 2009 11:47 am

Gina wrote:9 + 2y + x - 25 + 3 + x

In using the commutative property, when I move stuff around, is there a rule as to which order it should be in?

Unless they've given you a rule, no, there are only conventions. In general, it is expected that the variable terms go first, and in alphabetical order. So "the" answer would be:

. . . . .x + x + 2y + 9 + 3 - 25 = 2x + 2y - 13

Gina wrote:According to PEMDAS, I should do addition before subtraction.

Actually, addition and subtraction are at the same "level" or order of importance. Once you're down to just adding and subtracting, then you "should" work from left to right but, in practical terms, you would group in whatever manner you found most helpful. :wink:

Gina
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Re: Commutative, Associative Property Question

Postby Gina » Fri May 29, 2009 2:52 pm

Thank you very much!


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