Question 184
Let $a \gt b \gt c \gt d$ be positive integers and suppose
$$
ac + bd = (b + d + a - c)(b + d - a + c).
$$
Prove that $ab + cd$ is not prime.
$$
ac + bd = (b + d + a - c)(b + d - a + c).
$$
Prove that $ab + cd$ is not prime.
MathNet 2001 — Part 01 Question 184
Math Olympiad Vault · MathNet 2001 — Part 01