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How to Solve[] for a negative exponent?

Posted 10 years ago

How can I solve for 'x'?

I tried the following,

Solve[0.3^-x == 1, x]
NSolve[0.3^-x == 1, x]

The answer should be close to -2/11ths,

0.3^-2/11==1.0101

I'm interested in getting this specific form, of solving for a negative exponent, to work, rather than this example problem. Much thanks for help!

POSTED BY: Greg
2 Replies

The answer is 0

In[64]:= 0.3^0
Out[64]= 1.

because the right hand side is 1. More general

In[74]:= Solve[1/0.3^x == 1/817, x, Reals]
During evaluation of In[74]:= Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result. >>
Out[74]= {{x -> -5.56959}}

In[75]:= NSolve[0.3^(-x) == 1/817, x, Reals]
During evaluation of In[75]:= Solve::ratnz: Solve was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result. >>
Out[75]= {{x -> -5.56959}}

In[76]:= Rationalize[0.3^(-x) /. %75[[1, 1]]]
Out[76]= 1/817
POSTED BY: Udo Krause
Posted 10 years ago

smart- thanks

POSTED BY: Greg
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