\(A=131\cdot\left(35-27\right)-35\cdot31+131\cdot207\\ A=131\cdot35+131\cdot27-35\cdot31+131\cdot207\\ A=35\cdot\left(131-31\right)+131\cdot\left(27+207\right)\\ A=35\cdot100+131\cdot234\\ A=3500+30654=34154\)

A=131.(35−27)−35.31+131.207

A=131.35+131.27−35.31+131.207

A=35.(131−31)+131.(27+207)

A=35.100+131.234

A=3500+30654

A=34154

\(a,\dfrac{3}{4}-\dfrac{2}{7}=\dfrac{13}{28}\\ b,\dfrac{3}{8}-\dfrac{5}{16}=\dfrac{1}{16}\\ c,\dfrac{7}{5}-\dfrac{2}{3}=\dfrac{11}{15}\\ d,\dfrac{31}{36}-\dfrac{5}{6}=\dfrac{1}{36}\)

\(a,\dfrac{3}{4}-\dfrac{2}{7}=\dfrac{21}{28}-\dfrac{8}{28}=\dfrac{13}{28}\)

\(b,\dfrac{3}{8}-\dfrac{5}{16}=\dfrac{6}{16}-\dfrac{5}{16}=\dfrac{1}{16}\)

\(c,\dfrac{7}{5}-\dfrac{2}{3}=\dfrac{21}{15}-\dfrac{10}{15}=\dfrac{11}{15}\)

\(d,\dfrac{31}{36}-\dfrac{5}{6}=\dfrac{31}{36}-\dfrac{30}{36}=\dfrac{1}{36}\)

a) \(\dfrac{3}{4}-\dfrac{2}{7}=\dfrac{21-8}{28}=\dfrac{13}{28}\) 

b)\(\dfrac{3}{8}-\dfrac{5}{16}=\dfrac{6-5}{16}=\dfrac{1}{16}\) 

c)\(\dfrac{7}{5}-\dfrac{2}{3}=\dfrac{21-10}{15}=\dfrac{11}{15}\) 

d)\(\dfrac{31}{36}-\dfrac{5}{6}=\dfrac{31-30}{36}=\dfrac{1}{36}\)

......................?

mik ko biết

mong bn thông cảm 

nha ................

$\frac{-1}{2}-\frac{-3}{5}+\frac{-1}{9}+\frac{1}{131}-\frac{-2}{7}+\frac{4}{35}-\frac{7}{18}$

$=\frac{-1}{2}+\frac{3}{5}-\frac{1}{9}+\frac{1}{131}+\frac{2}{7}+\frac{4}{35}-\frac{7}{18}$

$=\frac{1}{10}-\frac{122}{1179}+\frac{2}{5}-\frac{7}{18}$

$=-\frac{41}{11790}+\frac{1}{90}$

$=\frac{1}{131}$

Bài 1: 

\(=\dfrac{-1}{2}+\dfrac{3}{5}-\dfrac{1}{9}+\dfrac{1}{131}+\dfrac{2}{7}+\dfrac{4}{35}-\dfrac{7}{18}\)

\(=\left(-\dfrac{1}{2}-\dfrac{1}{9}-\dfrac{7}{18}\right)+\left(\dfrac{3}{5}+\dfrac{2}{7}+\dfrac{4}{35}\right)+\dfrac{1}{131}\)

\(=\dfrac{-9-2-7}{18}+\dfrac{21+10+4}{35}+\dfrac{1}{131}\)

=1/131

Bài 2:

b: \(B=\dfrac{1}{99}-\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{98\cdot99}\right)\)

\(=\dfrac{1}{99}-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{98}-\dfrac{1}{99}\right)\)

\(=\dfrac{1}{99}-\dfrac{98}{99}=-\dfrac{97}{99}\)

Bài này mình làm xong rồi nhưng lỡ tay bấm nút hủy.

MONG CÁC BẠN  

\(\frac{-1}{2}-\frac{-3}{5}+\frac{-1}{9}+\frac{1}{131}-\frac{-2}{7}+\frac{4}{35}-\frac{7}{18}\)

\(=\frac{-1}{2}+\frac{3}{5}-\frac{1}{9}+\frac{1}{131}+\frac{2}{7}+\frac{4}{35}-\frac{7}{18}\)

\(=\frac{1}{10}-\frac{122}{1179}+\frac{2}{5}-\frac{7}{18}\)

\(=-\frac{41}{11790}+\frac{1}{90}\)

\(=\frac{1}{131}\)

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