7.3. The numbers $a, b$, and $c$ satisfy the relation $\frac{a+b}{c}=\frac{b+c}{a}=\frac{a+c}{b}$. Find $a+b+c$, given that $b \neq c$.
Answer: 0. Solution. From the equality $\frac{a+b}{c}=\frac{a+c}{b}$, we get $a(b-c)=(c-b)(c+b)$. Dividing this equality by $b-c \neq 0$, we obtain $b+c=-a$. Therefore, $a+b+c=0$.