Question 67
Let $a$, $b$, $c$, $d$ be integers such that $a \gt b \gt c \gt d \geq -2021$ and
$$
\frac{a + b}{b + c} = \frac{c + d}{d + a}
$$
(and $b + c \neq 0 \neq d + a$). What is the maximum possible value of $ac$?
$$
\frac{a + b}{b + c} = \frac{c + d}{d + a}
$$
(and $b + c \neq 0 \neq d + a$). What is the maximum possible value of $ac$?