Step-by-step explanation:
First, this is how I read it.
[tex]\log(x^{125})=-3[/tex]
Next, this is how logarithms work:
[tex]b^y=x\implies \log_b(x)=y[/tex]
In your equation, we have all 3 numbers:
With that information, you can convert the logarithm into "normal" form:
[tex]10^{-3}=x^{123}[/tex]
The negative power rule [tex]x^{-a}=\frac{1}{x^a}[/tex] is also useful here.
Now, just solve for x:
[tex]x^{125}=\frac{1}{10^3}\\x^{125}=\frac{1}{1000}\\x=\sqrt[125]{\frac{1}{1000}}\\x=\frac{1}{\sqrt[125]{1000} }[/tex]
That's about as simplified as it gets, unless you want this:
[tex]x=\frac{1}{10^{\frac{3}{125}}}[/tex]
Thats 10^(3/125), numbers got very small.
I'm still not confident I understood the problem correctly, so let me know if I need to fix anything.