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 October 27th, 2013, 03:47 PM #1 Newbie   Joined: Sep 2013 Posts: 17 Thanks: 0 Ring Hi . How I prove this ? : If R a ring with 1. Prove that $(-1)^2=1$ in R ? anny suggestions ?
October 27th, 2013, 05:29 PM   #2
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Quote:
 Originally Posted by sebaflores Hi . How I prove this ? : If R a ring with 1. Prove that $(-1)^2=1$ in R ? anny suggestions ?

(-1)(-1) - 1

= (-1)(-1) + (-1)

= (-1)(-1) + (-1)1

= (-1)(-1 + 1) by the distributive law

= (-1)0 = 0

so (-1)(-1) = 1

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