Show the following identities for a, b, c ∈ N.
(a) gcd(ca, cb) = c gcd(a, b) Hint: To show that two integers x,
y ∈ Z are equal you can show that both x | y and y | x which
implies x = y or x = −y. Thus, if both x and y have the same sign,
they must be equal.
(b) lcm(ca, cb) = c lcm(a, b)
(c) ab = lcm(a, b) gcd(a, b) Hint: Consider...