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A Reciprocal And Square Problem (Posted on 2007-07-10) |
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Find all real pairs (p, q) satisfying the following system of equations:
p - 1/p - q2 = 0
q/p + pq = 4
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Submitted by K Sengupta
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Rating: 3.5000 (2 votes)
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Solution:
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(Hide)
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The given equations yield;
p – 1/p = q^2
p+ 1/p = 4/q
Thus, 16/(q^2) – q^4 = 4, giving:
u^3 + 4u – 16 = 0, where u = q^2
Or, (u-2)(u^2 +2u +8) = 0
Or, u =2, ignoring the complex roots of u which are inadmissible.
or, q = +/- √2)
If q = √2, then p = (1/2)*(q^2 + 4/q) = 1+ √2
Similarly, q = - √2 gives p = 1 – √2
Thus (p, q) = (√2, 1 + √2), (-√2, 1- √2) are the only possible solutions.
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