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All possible real values (Posted on 2023-11-01) Difficulty: 3 of 5
Determine all possible real values of m such that:

3m * 21m2 = 21

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Solution Solution | Comment 1 of 3
The exact solution is a bit ugly, but it can be a little neater if we let a=log_3(21)=log(21)/log(3)

Taking the base 3 logarithm of both sides yields

m + am^2 = a

Which is a quadratic in m.  The solutions are then given by

m = (-1 +/1 sqrt(1+4a^2))/(2a)

I don't think this can be simplified much.  The approximate solutions are

m={-1.197, 0.836}

Checking my math
https://www.desmos.com/calculator/eunb9djkzt





  Posted by Jer on 2023-11-01 08:52:42
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