Solution:
First of all if (a,b,c) is a solution of the system then also (−a,−b,−c) is a solution. Hence we can suppose that abc>0. From the first condition we have
a+b+c=abcab+bc+ca
Now, from the first condition and the second condition we get
(a+b+c)2−(a2+b2+c2)=(a1+b1+c1)2−(a21+b21+c21)
The last one simplifies to
ab+bc+ca=abca+b+c
First we show that a+b+c and ab+bc+ca are different from 0. Suppose on contrary then from relation (1) or (2) we have a+b+c=ab+bc+ca=0. But then we would have
a2+b2+c2=(a+b+c)2−2(ab+bc+ca)=0
which means that a=b=c=0. This is not possible since a,b,c should be different from 0. Now multiplying (1) and (2) we have
(a+b+c)(ab+bc+ca)=(abc)2(a+b+c)(ab+bc+ca)
Since a+b+c and ab+bc+ca are different from 0, we get (abc)2=1 and using the fact that abc>0 we obtain that abc=1. So relations (1) and (2) transform to
a+b+c=ab+bc+ca.
Therefore,
(a−1)(b−1)(c−1)=abc−ab−bc−ca+a+b+c−1=0.
This means that at least one of the numbers a,b,c is equal to 1. Suppose that c=1 then relations (1) and (2) transform to a+b+1=ab+a+b⇒ab=1. Taking a=t then we have b=t1. We can now verify that any triple (a,b,c)=(t,t1,1) satisfies both conditions. t∈R∖{0}. From the initial observation any triple (a,b,c)=(t,t1,−1) satisfies both conditions. t∈R∖{0}. So, all triples that satisfy both conditions are (a,b,c)=(t,t1,1),(t,t1,−1) and all permutations for any t∈R∖{0}.