c) Ta có: \(\dfrac{3}{5}+\dfrac{-5}{20}+\dfrac{30}{75}+\dfrac{-7}{4}\)

\(=\dfrac{3}{5}+\dfrac{2}{5}+\dfrac{-1}{4}+\dfrac{-7}{4}\)

\(=1-2=-1\)

Giải:

a)-1/12+4/3=-1/12+16/12=15/12=5/4

b)(-4/14-3/15)-(1/5-20/35-(-1)).7

=-17/35-22/35.7

=-17/35-22/5

=-171/35

c)3/5+-5/20+30/75+-7/4

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

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

=1+-2

=-1

d)5/6.-12/14+7/13

=-5/7+7/13

=-16/91

e)2/-9-5/-36-1/4

=-1/12-1/4

=-1/3

f)2/23+-5/12+7/18+21/23+-7/12

=(2/23+21/23)+(-5/12+-7/12)+7/18

=1+-1+7/18

=7/18

xcsxccsz

Mọi người tk mình đi mình đang bị âm nè!!!!!!

Ai tk mình mình tk lại nha !!!

a.1/4

b.-7/144

c.25/21

d.17/7

e.80/63

f.9/7

a)1/4

b)-7/144

c)-25/21

d)17/7

e)16/63

f)9/7

ccccccccccch

Ghi đầy đủ nha

bn có thể ghi rõ ràng đc ko?

a)\(-\dfrac{3}{7}+\dfrac{5}{13}+\dfrac{3}{7}\) 

=\(\left(-\dfrac{3}{7}+\dfrac{3}{7}\right)+\dfrac{5}{13}\) 

=\(0+\dfrac{5}{13}\) 

=\(\dfrac{5}{13}\)

\(a.\)

\(\frac{4}{9}.x=\frac{1}{9}\)

\(\Rightarrow x=\frac{1}{9}:\frac{4}{9}\)

\(\Rightarrow x=\frac{1}{9}.\frac{9}{4}\)

\(\Rightarrow x=\frac{1}{4}\)

Vậy \(x=\frac{1}{4}\)

\(b.\)

\(\frac{7}{18}.x-\frac{2}{3}=\frac{5}{18}\)

\(\Rightarrow\frac{7}{18}.x=\frac{5}{18}+\frac{2}{3}\)

\(\Rightarrow\frac{7}{18}.x=\frac{5}{18}+\frac{12}{18}\)

\(\Rightarrow\frac{7}{18}.x=\frac{17}{18}\)

\(\Rightarrow x=\frac{17}{18}:\frac{7}{18}\)

\(\Rightarrow x=\frac{17}{18}.\frac{18}{7}\)

\(\Rightarrow x=\frac{17}{7}\)

Vậy \(x=\frac{17}{7}\)

\(c.\)

\(x:-\frac{1}{12}=\frac{7}{12}\)

\(\Rightarrow x=\frac{7}{12}.-\frac{1}{12}\)

\(\Rightarrow x=-\frac{7}{144}\)

Vậy \(x=-\frac{7}{144}\)

\(d.\)

\(\frac{4}{9}-\frac{7}{8}.x=-\frac{2}{3}\)

\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}-\left(-\frac{2}{3}\right)\)

\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}+\frac{2}{3}\)

\(\Rightarrow\frac{7}{8}.x=\frac{4}{9}+\frac{6}{9}\)

\(\Rightarrow\frac{7}{8}.x=\frac{10}{9}\)

\(\Rightarrow x=\frac{10}{9}:\frac{7}{8}\)

\(\Rightarrow x=\frac{10}{9}.\frac{8}{7}\)

\(\Rightarrow x=\frac{80}{63}\)

Vây \(x=\frac{80}{63}\)

\(e.\)

\(-\frac{5}{14}:x=-\frac{3}{10}\)

\(\Rightarrow x=-\frac{5}{14}:-\frac{3}{10}\)

\(\Rightarrow x=-\frac{5}{14}.-\frac{10}{3}\)

\(\Rightarrow x=\frac{5}{7}.\frac{5}{3}\)

\(\Rightarrow x=\frac{25}{21}\)

Vậy \(x=\frac{25}{21}\)

\(g.\)

\(\frac{1}{6}+\frac{-5}{7}:x=-\frac{7}{18}\)

\(\Rightarrow-\frac{5}{7}:x=-\frac{7}{18}-\frac{1}{6}\)

\(\Rightarrow-\frac{5}{7}:x=-\frac{7}{18}-\frac{3}{18}\)

\(\Rightarrow-\frac{5}{7}:x=-\frac{10}{18}\)

\(\Rightarrow-\frac{5}{7}:x=-\frac{5}{9}\)

\(\Rightarrow x=-\frac{5}{7}:-\frac{5}{9}\)

\(\Rightarrow x=-\frac{5}{7}.-\frac{9}{5}\)

\(\Rightarrow x=\frac{9}{7}\)

Vậy \(x=\frac{9}{7}\)

a) \(\dfrac{7}{-25}+\dfrac{8}{25}=\dfrac{-7}{25}+\dfrac{8}{25}=\dfrac{1}{25}\)

\(\dfrac{4}{5}+\dfrac{4}{-18}=\dfrac{4}{5+\left(-18\right)}=\dfrac{4}{-13}=\dfrac{-4}{13}\)

\(\dfrac{7}{21}+\dfrac{9}{-36}=\dfrac{1}{3}+\dfrac{1}{-4}=\dfrac{1}{3+\left(-4\right)}=\dfrac{1}{-1}=1\)

b) \(\dfrac{12}{20}-\dfrac{2}{5}=\dfrac{12}{20}+\left(\dfrac{-2}{5}\right)=\dfrac{3}{5}+\dfrac{-2}{5}=\dfrac{3+\left(-2\right)}{5}=\dfrac{1}{5}\)

\(\dfrac{2}{3}-\dfrac{-5}{6}=\dfrac{2}{3}+\dfrac{5}{6}=\dfrac{4}{6}+\dfrac{5}{6}=\dfrac{9}{6}=\dfrac{3}{2}\)

\(6-\dfrac{3}{20}=6+\dfrac{-3}{20}=\dfrac{60}{60}+\dfrac{-9}{60}=\dfrac{51}{60}\)

c) \(\dfrac{2}{21}.\dfrac{-7}{3}=\dfrac{2.\left(-1\right)}{7.3}=\dfrac{-2}{21}\)

\(\dfrac{27}{28}.\left(-21\right)=\dfrac{27.\left(-21\right)}{28}=\dfrac{-567}{28}\)

\(\dfrac{-15}{7}.\dfrac{-14}{25}=\dfrac{-3.\left(-2\right)}{1.5}=\dfrac{6}{5}\)

Tách từng câu ra giùm, như này ai giải nổi:)))))

B, -2/3+4/7=-2/21

Bài 1:

a; \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{7}{21}\) + (- \(\dfrac{10}{36}\) + \(\dfrac{11}{19}\)  + \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)

=  \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{1}{3}\) -\(\dfrac{10}{36}\) + \(\dfrac{11}{19}\) + \(\dfrac{1}{3}\) - \(\dfrac{5}{8}\)

= (\(\dfrac{5}{18}\) - \(\dfrac{10}{36}\)) + (\(\dfrac{8}{19}\) + \(\dfrac{11}{19}\)) - (\(\dfrac{1}{3}\) - \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)

= (\(\dfrac{5}{18}\) - \(\dfrac{5}{18}\)) + \(\dfrac{19}{19}\) - 0 - \(\dfrac{5}{8}\)

= 0 + 1 - \(\dfrac{5}{8}\)

= \(\dfrac{3}{8}\)

b; \(\dfrac{1}{13}\) + (\(\dfrac{-5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\)) - (\(\dfrac{12}{17}\) - \(\dfrac{5}{18}\) + \(\dfrac{7}{5}\))

= \(\dfrac{1}{13}\) - \(\dfrac{5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\) - \(\dfrac{12}{17}\) + \(\dfrac{5}{18}\) - \(\dfrac{7}{5}\)

= (\(\dfrac{1}{13}\) - \(\dfrac{1}{13}\)) + (\(\dfrac{12}{17}\) - \(\dfrac{12}{17}\)) + (-\(\dfrac{5}{18}\) + \(\dfrac{5}{18}\)) - \(\dfrac{7}{5}\)

= 0 + 0 + 0 - \(\dfrac{7}{5}\)

= - \(\dfrac{7}{5}\)

Bài 1 c;

   \(\dfrac{15}{14}\) - (\(\dfrac{17}{23}\) - \(\dfrac{80}{87}\) + \(\dfrac{5}{4}\)) + (\(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\))

=  \(\dfrac{15}{14}\) - \(\dfrac{17}{23}\) + \(\dfrac{80}{87}\) - \(\dfrac{5}{4}\) + \(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\)

= (\(\dfrac{15}{14}-\dfrac{15}{14}\)) + (\(-\dfrac{17}{23}+\dfrac{17}{23}\)) - (\(\dfrac{5}{4}\) - \(\dfrac{1}{4}\)) + \(\dfrac{80}{87}\)

= 0 + 0 - 1 + \(\dfrac{80}{87}\)

= - \(\dfrac{7}{87}\)

Bài 1 d; 

   \(\dfrac{1}{25}\) - \(\dfrac{4}{27}\) + (-\(\dfrac{23}{27}\) + \(\dfrac{-1}{25}\) - \(\dfrac{5}{43}\)) + \(\dfrac{5}{43}\) - \(\dfrac{4}{7}\)

= \(\dfrac{1}{25}\) - \(\dfrac{4}{27}\) - \(\dfrac{23}{27}\) - \(\dfrac{1}{25}\) - \(\dfrac{5}{43}\) + \(\dfrac{5}{43}\) - \(\dfrac{4}{7}\)

= (\(\dfrac{1}{25}\) - \(\dfrac{1}{25}\)) - (\(\dfrac{4}{27}\) + \(\dfrac{23}{27}\)) - (\(\dfrac{5}{43}\) - \(\dfrac{5}{43}\)) - \(\dfrac{4}{7}\)

= 0 - 1 - 0 - \(\dfrac{4}{7}\)

= \(\dfrac{-11}{7}\)