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Czech-Slovak-Polish Match

Czech Republic algebra

Problem

Solve the system of equations in the domain of the real numbers.
Solution
From the form of the equations it is immediate that . Two of the numbers have to be of the same sign; then the right-hand side of the equation where the ratio of these two numbers occurs is positive, hence so must be the corresponding left-hand side, which implies that the third of the numbers must also have the same sign as the first and the second. Thus either , or . Let us consider only the former case (the latter can be reduced to it by passing from the solution to the solution ).

Multiply the first two equations of the system by the expression and then subtract them; this gives, upon a small manipulation, . If a triple is a solution, then so are also the triples and ; thus we may assume that . Then and (remember that ), so the equality , together with the condition , implies that , which means that . The system then reduces to the single equation , which has a (unique) positive root .

Conclusion. The system has exactly two solutions, .
Final answer
x = y = z = ± sqrt(2)/2

Techniques

Simple Equations