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A couple of Logs (Posted on 2002-06-04) Difficulty: 4 of 5
logy(x) + logx(y) = 43

What are the values of x and y?

See The Solution Submitted by Dulanjana    
Rating: 2.4375 (16 votes)

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No unique solution | Comment 3 of 17 |
One equation, two unknowns. In general, that means an infinite number of solutions. I'll generate a couple (forgive the lack of subscripts):

logx(y) = logy(y)/logy(x) = 1/logy(x)

So from the original problem,

logy(x) + 1/logy(x) = 43

Let L = logy(x).

L + 1/L = 43

L^2 - 43L + 1 = 0

L = (43 +/- sqrt(43^2 - 4))/2

L has roots at 42.9767 and 0.02327, so logy(x) = 42.9767 or logy(x) = 0.02327. Either one will work (Note that these roots are reciprocals of one another).

One solution would be (2, 2^42.9767). Another would be (10, 10^42.9767). Still another would be (2^42.9767, 2). You get the idea.
  Posted by friedlinguini on 2002-06-04 06:57:17
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