Question 78
For three mutually distinct real numbers $a_1$, $a_2$, $a_3$, define three real numbers $b_1$, $b_2$, $b_3$ as follows:
$$
b_j = \left( 1 + \frac{a_j a_i}{a_j - a_i} \right) \left( 1 + \frac{a_j a_k}{a_j - a_k} \right), \quad \{i, j, k\} = \{1, 2, 3\}.
$$
Prove the inequality
$$
1 + |a_1 b_1 + a_2 b_2 + a_3 b_3| \le (1 + |a_1|)(1 + |a_2|)(1 + |a_3|).
$$
When does the equality hold?
$$
b_j = \left( 1 + \frac{a_j a_i}{a_j - a_i} \right) \left( 1 + \frac{a_j a_k}{a_j - a_k} \right), \quad \{i, j, k\} = \{1, 2, 3\}.
$$
Prove the inequality
$$
1 + |a_1 b_1 + a_2 b_2 + a_3 b_3| \le (1 + |a_1|)(1 + |a_2|)(1 + |a_3|).
$$
When does the equality hold?