Giải thích các bước giải:
Bài 1:
1) $\bigg(\dfrac{1}{3}\bigg)^2.\dfrac{1}{3}.9^2=\bigg(\dfrac{1}{3}\bigg)^3.81=\dfrac{1}{27}.81=3$
2) $\bigg(\dfrac{3}{7}\bigg)^{21}:\bigg(\dfrac{9}{41}\bigg)^6\\= \bigg(\dfrac{3}{7}\bigg)^{21}:\bigg(\dfrac{3}{12}\bigg)^{12}\\=\bigg(\dfrac{3}{7}\bigg)^{21-12}=\bigg(\dfrac{3}{7}\bigg)^{9}=\dfrac{19683}{40353607}$
3) $3-\bigg(-\dfrac{6}{7}\bigg)^6+\bigg(\dfrac{1}{2}\bigg)^2:2\\=3-\dfrac{46656}{117649}+\dfrac{1}{4}.\dfrac{1}{2}\\=\dfrac{306291}{117649}+\dfrac{1}{8}\\=\dfrac{2450328}{941192}+\dfrac{117649}{941192}=\dfrac{2567977}{941192}$
4) $\dfrac{5^4.20^4}{25^5.4^5}=\dfrac{(5.20)^4}{(25.4)^5}=\dfrac{100^4}{100^5}=\dfrac{1}{100}$
5) $\bigg(1+\dfrac{2}{3}-\dfrac{1}{4}\bigg).\bigg(\dfrac{4}{5}-\dfrac{3}{4}\bigg)^2\\=\bigg(\dfrac{12}{12}+\dfrac{8}{12}-\dfrac{3}{12}\bigg).\bigg(\dfrac{16}{20}-\dfrac{15}{20}\bigg)^2\\= \dfrac{17}{12}.\bigg(\dfrac{1}{20}\bigg)^2\\= \dfrac{17}{12}.\dfrac{1}{400}\\=\dfrac{17}{4800}$
