Tìm số hữu tỉ x, biết:
a) \({\left( {\dfrac{3}{7}} \right)^5}.x = {\left( {\dfrac{3}{7}} \right)^7}\);
b) \({(0,09)^3}:x = - {\rm{ }}{(0,09)^2}\).
Sử dụng công thức: \(x^m : x^n=x^{m-n} (m\ge n)\)
Advertisements (Quảng cáo)
a)
\(\begin{array}{l}{\left( {\dfrac{3}{7}} \right)^5}.x = {\left( {\dfrac{3}{7}} \right)^7}\\{\rm{ }}x = {\left( {\dfrac{3}{7}} \right)^7}:{\left( {\dfrac{3}{7}} \right)^5}\\{\rm{ }}x = {\left( {\dfrac{3}{7}} \right)^2} = \dfrac{9}{{49}}\end{array}\)
Vậy \(x = \dfrac{9}{{49}}\)
b)
\(\begin{array}{l}{(0,09)^3}:x = - {\rm{ }}{(0,09)^2}\\{\rm{ }}x = {(0,09)^3}:\left[ { - {\rm{ }}{{(0,09)}^2}} \right]\\{\rm{ }}x = - \left[ {{{(0,09)}^3}:{{(0,09)}^2}} \right]\\{\rm{ }}x = - {\rm{ }}0,09\end{array}\)
Vậy \(x = - {\rm{ }}0,09\).