Bài 70:
\(a.\sqrt{\dfrac{25}{81}.\dfrac{16}{49}.\dfrac{196}{9}}=\sqrt{\left(\dfrac{5}{9}\right)^2}.\sqrt{\left(\dfrac{4}{7}\right)^2}.\sqrt{\left(\dfrac{14}{3}\right)^2}=\dfrac{5}{9}.\dfrac{4}{7}.\dfrac{14}{3}=\dfrac{40}{27}\)
\(b.\sqrt{3\dfrac{1}{16}.2\dfrac{14}{25}.2\dfrac{34}{81}}=\sqrt{\dfrac{49}{16}.\dfrac{64}{25}.\dfrac{196}{81}}=\sqrt{\left(\dfrac{7}{4}\right)^2}.\sqrt{\left(\dfrac{8}{5}\right)^2}.\sqrt{\left(\dfrac{14}{9}\right)^2}=\dfrac{7}{4}.\dfrac{8}{5}.\dfrac{14}{7}=\dfrac{196}{45}\)
\(c.\dfrac{\sqrt{640}.\sqrt{34,3}}{\sqrt{567}}=\dfrac{\sqrt{640.34,3}}{\sqrt{567}}=\dfrac{\sqrt{8^2.7^2.7}}{\sqrt{\left(3^2\right)^2.7}}=\dfrac{8.7}{9}=\dfrac{56}{9}\)
\(d.\sqrt{21,6}.\sqrt{810}.\sqrt{11^2-5^2}=\sqrt{21,6.810.\left(11-5\right)\left(11+5\right)}=\sqrt{216.81.16.6}=\sqrt{1296.81.16}=\sqrt{\left(36.9.4\right)^2}=36.9.4=1296\)
