# Equation soluble (number theory)

1. Oct 20, 2013

### Funky1981

1. The problem statement, all variables and given/known data
p is an odd prime

(a) show that x^2+y^2+1=0 (mod p) is soluble

(b) show that x^2+y^2+1=0 (mod p) is soluble for any squarefree odd m

2. Relevant equations
For (a) hint given : count the integers in {0,1,2,...,p-1} of the form x^2 modulo p and those of the form -1-y^2 modulo p

can anyone help me ?? thanks!

2. Oct 20, 2013

### Dick

Ok, here's another hint. If a^2 and b^2 are the same mod p, then a^2-b^2=0 mod p. So (a-b)(a+b)=0 mod p. What can you conclude about the relation between a and b and why?

3. Oct 21, 2013

### Funky1981

thanks, i have solved the (a) part. For (b), I got the idea that since m is squarefree odd, so i write m = p1p2p3.... (pi are prime) then by (a) the eqation has solution for every pi. but how can i conclude that it has solution for their product???( btw , i made a mistake for typing, for (b) it should be modulo m but not p)

4. Oct 21, 2013

### Dick

I see the OP got a hint on another forum. You can use the Chinese Remainder Theorem to take the solutions for p1, p2, ... and use them to construct a solution for the case mod m. Wish I had thought of it.