Đáp án:

Giải thích các bước giải:

a) 16/15 . ( -5 )/14 . 54/24 . 56/21

= 4.2.2/5.3 . ( -5)/2.7 . 3.3/4 . 8/3

= 4.2.2.(-5).3.3.8/5.3.2.7.4.3

= -16/7

b) 7/3 . (-5)/2 . 15/21 . 4/(-5)

= 7/3 . ( -5)/2 . 5/7 . 2.2/(-5)

= 7.(-5).5.2.2/3.2.7.(-5)

= 10/3

#andy

\[\begin{array}{l}
a)\dfrac{{16}}{{15}}.\dfrac{{ - 5}}{{14}}.\dfrac{{54}}{{24}}.\dfrac{{56}}{{21}}\\
 = \dfrac{{16}}{{15}}.\dfrac{{ - 5}}{{14}}.\dfrac{9}{4}.\dfrac{8}{3}\\
 = \dfrac{{16.\left( { - 5} \right).9.8}}{{15.14.4.3}}\\
 = \dfrac{{ - 5760}}{{1520}}\\
 =  - \dfrac{{16}}{7}\\
b)\dfrac{7}{3}.\dfrac{{ - 5}}{2}.\dfrac{{15}}{{21}}.\dfrac{4}{{ - 5}}\\
 = \dfrac{7}{3}.\dfrac{{ - 5}}{2}.\dfrac{5}{7}.\dfrac{4}{{ - 5}}\\
 = \dfrac{{7.\left( { - 5} \right).5.4}}{{3.2.7.\left( { - 5} \right)}}\\
 = \dfrac{{ - 700}}{{ - 210}}\\
 = \dfrac{{10}}{3}
\end{array}\]