Math Is Fun Forum

Al-Allo

Member

Registered: 2012-08-23

Posts: 324

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 ???

Nehushtan

Member

Registered: 2013-03-09

Posts: 957

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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Al-Allo

Member

Registered: 2012-08-23

Posts: 324

Re: Question on associativity.

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

Bob

Administrator

Registered: 2010-06-20

Posts: 10,643

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

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