Упростить b^-7/b^-4*b^-2 при b=-1/5

[latex] \frac{b^{-7}}{b^{-4}*b^{-2}}=b^{-7-(-4-2)}=b^{-7+6}=b^{-1}= \frac{1}{b} \\ \frac{1}{b} =\frac{1}{ \frac{-1}{5} }=-5 [/latex]

[latex] \frac{b^{-7} }{b^{-5}} *b^{-2}=b^{-7-(-5)-2}=b^{-4}\\\\b= -\frac{1}{5}\\\\(- \frac{1}{5})^{-4}=(-5)^4=625[/latex]