Find the greatest common divisor in of 11 plus 7i and 18-i?

Answer 1

Use the division algorithm. If b = pa + r, then gcd(b,a) = gcd(a,r). Then you can apply the division algorithm again with a = qr + r' and gcd(a,r) = gcd(r, r'). Note that each time the square norm of the remainder gets smaller and smaller, so eventually this process will terminate and you can get the answer. Here, it should be 1.