My problem is:
Prove that there are no integers x and y such that x^2 − 5y^2 = 2.
Hint: consider this equation modulo 5.
I don't get how to start this with using modulo 5.
do I make the whole equation divisible by 5?
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Consider all possibilities. x will be one of the following :
for some suitable k.
What remainders do these leave when squared and divided by 5 ?
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