Tìm số hữu tỉ x, biết: ( 3/7)^5; x = ( 3/7)^7

Lời giải:

\({\left( {\frac{3}{7}} \right)^5}\,.\,x = {\left( {\frac{3}{7}} \right)^7}\)

\(x = {\left( {\frac{3}{7}} \right)^7}:{\left( {\frac{3}{7}} \right)^5}\)

\(x = {\left( {\frac{3}{7}} \right)^{7\, - \,5}}\)

\(x = {\left( {\frac{3}{7}} \right)^2}\)

\(x = \frac{9}{{49}}\).

Vậy \(x = \frac{9}{{49}}\).