(3/7) mũ 21 : (9/49) mũ 6

${(\dfrac{3}{7})^{21}:(\dfrac{9}{49})^{6} }$

=${(\dfrac{3}{7})^{21}:(\dfrac{3^2}{7^2})^{6} }$

=${(\dfrac{3}{7})^{21}: [(\dfrac{3}{7})^2]^6}$

=${(\dfrac{3}{7})^{21}:(\dfrac{3}{7})^{12} }$

=($\dfrac{3}{7}$ )$^{9}$