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Hello Operator (Posted on 2003-10-17) Difficulty: 4 of 5
Consider a binary operation # that is closed under the set of integers (if a and b are integers, then a#b is an integer).

Assume that, for all integers a and b, it is true that (a#b)#a=b.

Prove that a#(b#a)=b.

See The Solution Submitted by DJ    
Rating: 4.2727 (11 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: freaky solution | Comment 18 of 19 |
(In reply to freaky solution by Victor Zapana)

Your proof has a serious problem. Given only the information in the problem, it is not guaranteed that an inverse operator (your @) even exists.

Also, when you apply # B to each side (from line 3 to 4 in your proof), you assumed the commutative property was true and put B on the left.
  Posted by Brian Smith on 2003-10-29 13:12:08

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