Sum of two squares & Integers modulo 8 proof

jessica098

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Joined
Oct 20, 2008
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The problem I need help with is writing (and proving) a proposition about integers that are the sum of two squares.

I've found that if [a] is in integers modulo 8 (Z8), then the possible values for [a]^2 are 0, 1 and 4.

With that, I determined that if and [c] are in Z8, then the possible values of (^2+[c]^2) in Z8 are 0, 1, 2, 4, and 5 because:

0+0=0
0+1=1
0+4=4
1+0=1
1+1=2
1+4=5
4+0=4
4+1=5
4+4=8=0

What I'm asked to do now is complete the following proposition and prove it:

"For each integer a, if a is the sum of two squares, then ______."

I was given the following hint: The conclusion that you use should state something about what the integer a can be congruent to modulo 8.

Can anyone help me finish AND prove the proposition? I'm STUCK! Thank you in advance!!!!!!
 
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