Find all positive real-valued solutions to ⎩⎨⎧x−y+z1=2013,y−z+x1=2013,z−x+y1=2013.
Solutions — 2
Solution 1
Suppose w.l.o.g. that z≥x and z≥y. From the second equation x1≥2013,
therefore x≤20131. From the third equation y1≤2013, due to which y≥20131≥x. But now from the first equation z1≥2013, therefore z≤20131. Since we assumed that z≥y≥20131, the only possibility is z=y=20131, then also x=20131.
Solution 2
Adding up all the equations, we get x1+y1+z1=3⋅2013. Multiplying the first equation by z, the second one by x and third one by y and adding together we get 3=2013(x+y+z). Therefore the arithmetic and harmonic mean of x,y,z are both equal to 20131. Consequently x=y=z=20131.
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