ax b (mod n)

Given a, b, n > 0; find x.

Let d = gcd(a, n)

Solvable iff d b

**Theorem 31.23** If d b and d = ax' + ny' (as computed by
Extended-Euclid) then one solution is *x*_{0} = x'(b/d) mod n.

**Theorem 31.24** Given one solution *x*_{0}, there are exactly d distinct
solutions, modulo n, given by
for i = 0, 1, 2, , d-1.