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#1 2013-10-12 03:32:44

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Question on associativity.

Hey, I just have a question concerning associativity :

I have :

  by associativity

And I needed to prove each of my steps concerning an exercise. What I found weird was in the correction part, they justify the retreat of parentheses by saying "associativty" I thought that associativity was only used when you needed to add parentheses, or it can go in both ways ? Could anyone confirm it ???

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#2 2013-10-12 04:03:56

Nehushtan
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From: London
Registered: 2013-03-09
Posts: 606
Website

Re: Question on associativity.

You need parentheses on the RHS. You probably mean

i.e. sum the RHS terms from left to right.


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#3 2013-10-12 04:14:56

Al-Allo
Member
Registered: 2012-08-23
Posts: 290

Re: Question on associativity.

No, it is exactly the way I've put it in my first post ^^

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#4 2013-10-12 19:11:27

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,121

Re: Question on associativity.

hi Al-Allo

The rule for associativity is:

Nehushtan is absolutely right;  associativity applies to binary operations; that is to say, two elements combined to make one; so a four element expression doesn't exist.

I assume that the questioner intends the four element expression means 'add' elements in pairs in order going left to right hence

combine a + b, then the result with c; then that result with d.  This is what Nehushtan has written.

So how do you do it?

treat (a + b) as P; c as Q; d as R

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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