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Take Second Degree, Solve For Real (Posted on 2007-04-27) |
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Determine all possible real pairs (m,n) satisfying the following
system of equations:
mn2 = 15m2+ 17mn + 15n2
m2n = 20m2 + 3n2
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Submitted by K Sengupta
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Rating: 3.0000 (1 votes)
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Solution:
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Multiplying the first equation by m and the second equation by n and subtracting the second result from the first we obtain:
15m^3 - 3*m^2*n + 15m*n^2 - 3*n^3 = 0
Or, 5m^3 - m^2*n + 5m*n^2- n^3 = 0
Or, (5m-n)(m^2 + n^2) = 0;
Now, if, m^2 + n^2 = 0 then m is imaginary whenever n is real and vice versa.This is a contradiction.
Accordingly, 5m = n, and substituting this in the second equation, we obtain:
5*m^3 = 95*m^2; so that :
Either, m = 0; giving n = 0
Or, m= 19; giving n = 95
Consequently, (m, n) = (0,0); (19, 95) are the only possible solutions to the given problem.
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