\(\dfrac{3}{4}:2=\dfrac{3}{4}\times\dfrac{1}{2}=\dfrac{3}{8}\)

3/4:2=0,735

\(\dfrac{2}{3}\times\dfrac{6}{7}=\dfrac{12}{21}=\dfrac{4}{7}\)

#DatNe

    \(\dfrac{2}{3}\) \(\times\) \(\dfrac{6}{7}\)

=  \(\dfrac{4}{7}\)

\(\dfrac{5}{6}\times3+\dfrac{20}{6}\times2-1:\dfrac{6}{5}\)
\(=\dfrac{5}{6}\times3-\dfrac{5}{6}+\dfrac{20}{6}\times2\)
\(=\dfrac{5}{6}\times\left(3-1\right)+\dfrac{20}{6}\times2\)
\(=\dfrac{5}{6}\times2+\dfrac{20}{6}\times2\)
\(=\left(\dfrac{5}{6}+\dfrac{20}{6}\right)\times2\)
\(=\dfrac{25}{6}\times2\)
\(=\dfrac{25}{3}\)

#DatNe

\(\dfrac{5}{6}\) \(\times\) 3 + \(\dfrac{20}{6}\) \(\times\) 2 - 1 : \(\dfrac{6}{5}\)

= \(\dfrac{5}{6}\) \(\times\) 3 + \(\dfrac{20}{6}\) \(\times\) 2 - \(\dfrac{5}{6}\)

= \(\dfrac{5}{6}\) \(\times\) 3 + \(\dfrac{5}{6}\) \(\times\) 8 - \(\dfrac{5}{6}\) \(\times\)1

= \(\dfrac{5}{6}\) \(\times\) ( 3 + 8 - 1)

= \(\dfrac{5}{6}\) \(\times\)10

= \(\dfrac{25}{3}\)

\(\dfrac{20}{16}-\dfrac{3}{4}=\dfrac{5}{4}-\dfrac{3}{4}=\dfrac{2}{4}=\dfrac{1}{2}\)
#DatNe

20/16=5/4

5/4-2/4=3/4

y x \(\dfrac{1}{3}\) = 6

y = 6 : \(\dfrac{1}{3}\)

y = 18

\(y\times\dfrac{1}{3}=6\)
\(y=6:\dfrac{1}{3}\)
\(y=6\times3=18\)
#DatNe

\(\dfrac{3}{15}+\dfrac{2}{5}=\dfrac{1}{5}+\dfrac{2}{5}=\dfrac{3}{5}\)
#DatNe

\(\dfrac{3}{15}+\dfrac{2}{5}=\dfrac{1}{5}+\dfrac{2}{5}=\dfrac{3}{5}\)

TH1: \(a+b+c=0\Rightarrow\left\{{}\begin{matrix}a+b=-c\\b+c=-a\\c+a=-b\end{matrix}\right.\)

\(\Rightarrow\dfrac{\left(a+b\right)\left(b+c\right)\left(c+a\right)}{abc}=\dfrac{\left(-c\right).\left(-a\right).\left(-b\right)}{abc}=-1\)

TH2: \(a+b+c\ne0\)

Áp dụng dãy tỉ lệ thức bằng nhau:

\(\dfrac{a+b-c}{c}=\dfrac{c+a-b}{b}=\dfrac{b+c-a}{a}=\dfrac{a+b-c+c+a-b+b+c-a}{a+b+c}=1\)

\(\Rightarrow\left\{{}\begin{matrix}a+b-c=c\\c+a-b=b\\b+c-a=a\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a+b=2c\\c+a=2b\\b+c=2a\end{matrix}\right.\)

\(\Rightarrow a=b=c\)

\(\Rightarrow\dfrac{\left(a+b\right)\left(b+c\right)\left(c+a\right)}{abc}=\dfrac{2a.2a.2a}{a^3}=8\)

Vậy biểu thức đã cho bằng -1 hoặc bằng 8

s can son la:

0,6 x 0,6 x 5 x 2 = 3,6 (m3)

5/7=5x9/7x9=45/63

4/9=4x7/9x7=28/63

=>đáp án B

C

\(\dfrac{1}{2}\times\dfrac{3}{4}:\dfrac{6}{5}=\dfrac{3}{8}:\dfrac{6}{5}=\dfrac{5}{16}\)

\(\dfrac{2}{3}+\dfrac{1}{6}:\dfrac{7}{12}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{14}{21}+\dfrac{6}{21}=\dfrac{20}{21}\)

\(8\times\dfrac{3}{5}:\dfrac{12}{5}=\dfrac{24}{5}:\dfrac{12}{5}=2\)

\(\dfrac{4}{9}+\dfrac{3}{4}-\dfrac{1}{3}=\dfrac{16}{36}+\dfrac{27}{36}-\dfrac{12}{36}=\dfrac{31}{36}\)