Giải thích các bước giải:
$\text{Bài 1:}$
$a)(\dfrac{5}{6}-\dfrac{1}{3})(\dfrac{2}{10}-\dfrac{2}{5})^2$
$=(\dfrac{5}{6}-\dfrac{2}{3})(\dfrac{1}{5}-\dfrac{2}{5})^2$
$=\dfrac{3}{6}.(-\dfrac{1}{5})^2$
$=\dfrac{1}{2}.\dfrac{1}{25}$
$=\dfrac{1}{50}$
$b)\dfrac{2^{17}.9^5}{6^7.8^4}$
$=\dfrac{2^{17}.3^{10}}{3^7.2^7.2^{12}}$
$=\dfrac{2^{17}.3^{10}}{3^7.2^{19}}$
$=\dfrac{3^3}{2^2}$
$=\dfrac{27}{4}$
$\text{Bài 2:}$
$\dfrac{x}{12}=\dfrac{-5}{4}$
$⇔4x=(-5).12$
$⇔4x=-60$
$⇔x=-15$
$\text{Vậy $x=-15$}$
$\text{Bài 3:}$
$24.7=2.84$
$⇒\dfrac{24}{2}=\dfrac{84}{7}$
$⇒\dfrac{2}{24}=\dfrac{7}{84}$
$⇒\dfrac{2}{7}=\dfrac{24}{84}$
$⇒\dfrac{7}{2}=\dfrac{84}{24}$
Học tốt!!!
