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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

Hey, I just have a question concerning associativity :

I have :

by associativityAnd 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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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 324

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

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,767

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

Children are not defined by school ...........The Fonz

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

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