\(\dfrac{-1}{7}-\dfrac{1}{8}=\dfrac{-8}{56}-\dfrac{7}{56}=\dfrac{-15}{56}\\ \dfrac{-15}{48}-\dfrac{1}{12}=\dfrac{-5}{16}-\dfrac{1}{12}=\dfrac{-15}{48}-\dfrac{4}{48}=\dfrac{-19}{48}\\ \dfrac{-3}{4}-\dfrac{4}{5}=\dfrac{-15}{20}-\dfrac{16}{20}=\dfrac{-31}{20}\\ \dfrac{3}{4}+\dfrac{-5}{6}-\dfrac{11}{12}=\dfrac{9}{12}-\dfrac{10}{12}-\dfrac{11}{12}=\dfrac{-12}{12}=-1\)

banj xem lại câu 2 với câu 4 nhé

1: \(\frac{-5}{7}\cdot\frac{2}{11}+\frac{-5}{7}\cdot\frac{9}{11}+1\frac57\)

\(=-\frac57\left(\frac{2}{11}+\frac{9}{11}\right)+1+\frac57\)

\(=-\frac57+1+\frac57=1\)

2: \(-3\frac{4}{13}\cdot15\frac{3}{41}+3\frac{4}{13}\cdot2\frac{3}{41}\)

\(=3\frac{4}{13}\left(-15-\frac{3}{41}+2+\frac{3}{41}\right)\)

\(=\frac{43}{13}\cdot\left(-13\right)=-43\)

3: \(\frac45\cdot15\frac14-\frac45\cdot15\frac13+\frac{11}{30}\)

\(=\frac45\left(15+\frac14-15-\frac13\right)+\frac{11}{30}\)

\(=\frac45\cdot\left(\frac14-\frac13\right)+\frac{11}{30}\)

\(=\frac45\cdot\frac{-1}{12}+\frac{11}{30}=\frac{-1}{15}+\frac{11}{30}=\frac{-2}{30}+\frac{11}{30}=\frac{9}{30}=\frac{3}{10}\)

4: \(\frac{4}{20}+\frac{16}{42}+\frac{6}{15}-\frac35+\frac{2}{21}-\frac{10}{21}+\frac{3}{10}\)

\(=\left(\frac15+\frac25-\frac35\right)+\left(\frac{8}{21}+\frac{2}{21}-\frac{10}{21}\right)+\frac{3}{10}\)

=0+0+\(\frac{3}{10}=\frac{3}{10}\)

1: \(=\dfrac{16}{15}\left(-\dfrac{4}{9}+\dfrac{3}{7}\right)+\dfrac{16}{15}\left(\dfrac{4}{7}-\dfrac{5}{9}\right)\)

\(=\dfrac{16}{15}\left(-\dfrac{4}{9}+\dfrac{3}{7}+\dfrac{4}{7}-\dfrac{5}{9}\right)=0\)

2: \(=\dfrac{29}{9}\left(15+\dfrac{4}{7}-8-\dfrac{1}{7}+\dfrac{15}{7}-\dfrac{1}{7}\right)\)

\(=\dfrac{20}{9}\cdot\left(7\cdot\dfrac{18}{7}\right)=\dfrac{20}{9}\cdot18=40\)

a: \(A=\dfrac{-7}{28}\cdot\dfrac{15}{25}=\dfrac{-1}{4}\cdot\dfrac{3}{5}=\dfrac{-3}{20}\)

b: \(B=\dfrac{-5\cdot7}{14\cdot\left(-3\right)}=\dfrac{35}{42}=\dfrac{5}{6}\)

c: \(C=\dfrac{-1}{5}-\dfrac{1}{5}\cdot\dfrac{3}{5}=\dfrac{-1}{5}-\dfrac{3}{25}=\dfrac{-8}{25}\)

d: \(D=\dfrac{-3}{4}-\dfrac{1}{4}=-1\)

e: \(E=\dfrac{-4}{5}\left(1-\dfrac{15}{16}\right)=\dfrac{-4}{5}\cdot\dfrac{1}{16}=\dfrac{-1}{20}\)

f: \(F=\dfrac{6-7}{4}\cdot\dfrac{4+12}{22}=\dfrac{-1}{4}\cdot\dfrac{8}{11}=\dfrac{-2}{11}\)

a: \(-\frac47+\frac{15}{4}-\left(\frac{11}{4}+\frac37+\frac12-\frac13\right)\)

\(=-\frac47+\frac{15}{4}-\frac{11}{4}-\frac37-\left(\frac12-\frac13\right)\)

\(=\left(-\frac47-\frac37\right)+\left(\frac{15}{4}-\frac{11}{4}\right)-\frac16=\left(-1\right)+1-\frac16=-\frac16\)

b: \(\frac15\left(\frac12-\frac13\right):\left(-\frac{9}{10}\right)+\frac{-7}{3}\)

\(=\frac15\cdot\frac16\cdot\frac{10}{-9}+\frac{-7}{3}=\frac{1}{3\cdot\left(-9\right)}+\frac{-7}{3}\)

\(=-\frac{1}{27}-\frac73=-\frac{1}{27}-\frac{63}{27}=-\frac{64}{27}\)

c: \(-\frac{20}{23}+\frac23-\frac{3}{23}+\frac25+\frac{7}{15}\)

\(=\left(-\frac{20}{23}-\frac{3}{23}\right)+\left(\frac23+\frac25+\frac{7}{15}\right)\)

\(=-1+\frac{10+6+7}{15}=-1+\frac{23}{15}=\frac{8}{15}\)

a: Ta có: \(\dfrac{8}{9}-\left(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+...+\dfrac{1}{72}\right)\)

\(=\dfrac{8}{9}-\left(1-\dfrac{1}{2}+\dfrac{1}{2}+\dfrac{1}{3}-...+\dfrac{1}{8}-\dfrac{1}{9}\right)\)

=0

câu b, đâu ạ?

-2/15

-4/35

-5/3

10

-8/3

-7/2

-9

-4/3

Chúc em học giỏi

\(=\dfrac{-2}{15}\\ =\dfrac{-4}{35}\\ =-1\\ =10\\ =\dfrac{-8}{3}\\ =-7\\ =-9\\ =\dfrac{-4}{3}\)

a: \(1-\left(5\dfrac{4}{9}+a-7\dfrac{7}{18}\right):15\dfrac{3}{4}=0\)

=>\(\left(5+\dfrac{4}{9}+a-7-\dfrac{7}{18}\right):\dfrac{63}{4}=1\)

=>\(\left(a-2+\dfrac{1}{18}\right)=\dfrac{63}{4}\)

=>\(a-\dfrac{35}{18}=\dfrac{63}{4}\)

=>\(a=\dfrac{63}{4}+\dfrac{35}{18}=\dfrac{637}{36}\)

b: \(B=\left(\dfrac{2}{15}+\dfrac{5}{3}-\dfrac{3}{5}\right):\left(4\dfrac{2}{3}-2\dfrac{1}{2}\right)\)

\(=\dfrac{2+5\cdot5-3^2}{15}:\left(4+\dfrac{2}{3}-2-\dfrac{1}{2}\right)\)

\(=\dfrac{2+4^2}{15}:\left(2+\dfrac{2}{3}-\dfrac{1}{2}\right)\)

\(=\dfrac{18}{15}:\dfrac{13}{6}=\dfrac{6}{5}\cdot\dfrac{6}{13}=\dfrac{36}{65}\)

`@` `\text {Ans}`

`\downarrow`

`j)`

`-3/4 + 2/7 + (-1)/4 + 3/5 + 5/7`

`= (-3/4 - 1/4) + (2/7 + 5/7) + 3/5`

`= -1 + 1 + 3/5`

`= 3/5`

`k)`

`-2/17 + 15/23 + (-15)/17 + 4/19 + 8/23`

`= (-2/17 - 15/17) + (15/23 + 8/23) + 4/19`

`= -1 + 1 + 4/19`

`= 4/19`

$#KDN040510$

j: =-3/4-1/4+2/7+5/7+3/5

=-1+1+3/5

=3/5

k: =-2/17-15/17+15/23+8/23+4/19

=-1+1+4/19

=4/19