Question 4
Positive real numbers $a$, $b$, $c$, $d$ satisfy the relations
$$
abcd = 4, \quad a^2 + b^2 + c^2 + d^2 = 10.
$$
Determine the largest possible value of the expression $ab + bc + cd + da$.
$$
abcd = 4, \quad a^2 + b^2 + c^2 + d^2 = 10.
$$
Determine the largest possible value of the expression $ab + bc + cd + da$.