Find all triples of real numbers satisfying the system
Solutions — 2
Solution 1
It is easy to see that the triples and satisfy the system. We will show that there are no other solutions.
From the equations
it follows that if , then, from (1) , and from (2) . Similarly, if , then and . Further assume that none of , and equals or .
Factor the right-hand sides of (1), (2), (3) and multiply the results:
Reducing by , we get
Note that if , then, according to (1), and, according to (2), . In this case all factors in the right-hand side of (*) are greater than corresponding factors in the left-hand side — a contradiction.
Now factor the left-hand sides of equations (1), (2) and (3), and subtracting 1 from both sides of these equations, we obtain the equations
Note that if , then, according to (4), and, according to (5), . In this case all factors in the right-hand side of (*) are less than corresponding factors in the left-hand side — a contradiction.
It remains to consider the case, when and belong to the interval and, in particular, are negative. Again, all factors in the right-hand side of (*) are greater than corresponding factors in the left-hand side. So, there are no other solutions.
Solution 2
Consider the values of polynomials and on the intervals , and .
If , then . From the equations of the system successively obtain the inequalities , and , whence .
If , then and , hence . From the equations of the system we obtain the inequalities , and , and again .
If , then and , therefore . From the system we obtain the inequalities , and , whence again .
In all three cases we got a contradiction and the two remaining variants and easily lead us to the triples from the answer.