Question 98
Find all quadruples $(a,b,c,d)$ of real numbers satisfying
$$\begin{aligned}ab+c+d&=3,\\bc+d+a&=5,\\cd+a+b&=2,\\da+b+c&=6.\end{aligned}$$
$$\begin{aligned}ab+c+d&=3,\\bc+d+a&=5,\\cd+a+b&=2,\\da+b+c&=6.\end{aligned}$$
MathNet 2013 Question 98
Math Olympiad Vault · MathNet 2013