Logarithm Inequality: Solving 3(1-3^x) < 5^x(1-3^x)

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SUMMARY

The inequality 3(1-3^x) < 5^x(1-3^x) requires careful consideration of the conditions under which 1-3^x is positive or negative. The correct approach involves analyzing the intervals defined by the roots of the factors, leading to the conclusion that the solution set is 0 < x < log(5,3). The discussion clarifies that one cannot assume 1-3^x > 0 without justification, emphasizing the need to evaluate both cases separately.

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Homework Statement


3 - 3^(x+1) < 5^x - 15^x

3(1-3^x) < 5^x(1-3^x)

Do I have to impose 1-3^x > 0 ?

It results x<0 and x>log(5,3) but book has written 0 < x < log(5,3) where did I wrong ?
 
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hi scientifico! :smile:

(try using the X2 button just above the Reply box :wink:)
scientifico said:
Do I have to impose 1-3^x > 0 ?

no, you can't do that, you don't know that it's true!

either you must deal separately with 1-3x > 0 and 1-3x < 0.

or just write (1-3x)(3-5x) < 0 :wink:
 

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