\(a,\\ =\dfrac{5}{4}-\dfrac{3}{4}=\dfrac{2}{4}=\dfrac{1}{2}\\ b,\\ =\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{10-6}{15}=\dfrac{4}{15}\\ c,\\ =\dfrac{5}{6}-\dfrac{1}{4}=\dfrac{20-6}{24}=\dfrac{14}{24}=\dfrac{7}{12}\\ d,\\ =\dfrac{4}{3}-\dfrac{1}{4}=\dfrac{12-3}{12}=\dfrac{9}{12}=\dfrac{3}{4}\)

 cảm ơn chị ạ

a: =5/4-3/4=2/4=1/2

b: =30/45-18/45=12/45=4/15

c: =10/12-9/12=1/12

d: =4/3-1/4=16/12-3/12=13/12

a) \(\dfrac{-3}{20}\) + \(\dfrac{-7}{4}\) =\(\dfrac{-3}{20}\) + \(\dfrac{-35}{20}\) = -2

b) 6 và \(\dfrac{2}{3}\) - 4 và \(\dfrac{2}{3}\) = 2

c) \(\dfrac{-3}{10}\) + \(\dfrac{7}{12}\) = \(\dfrac{-18}{60}\) + \(\dfrac{35}{60}\) =\(\dfrac{17}{60}\)

d) \(\dfrac{35}{-9}\) . \(\dfrac{81}{7}\) = \(\dfrac{-35}{9}\) . \(\dfrac{81}{7}\) = 45

e) \(\dfrac{-2}{5}\) - \(\dfrac{-3}{4}\) = \(\dfrac{-8}{20}\) - \(\dfrac{-15}{20}\) = \(\dfrac{-8}{20}\) + \(\dfrac{15}{20}\) =\(\dfrac{7}{20}\)

f) \(\dfrac{5}{23}\) . \(\dfrac{7}{26}\) + \(\dfrac{5}{23}\) .\(\dfrac{9}{26}\) = \(\dfrac{5}{23}\) .  ( \(\dfrac{7}{26}\) + \(\dfrac{9}{26}\) )= \(\dfrac{5}{23}\) . \(\dfrac{8}{13}\) = \(\dfrac{40}{299}\)

g) \(\dfrac{-3}{12}\) : \(\dfrac{4}{15}\) =\(\dfrac{-3}{12}\) . \(\dfrac{15}{4}\) =\(\dfrac{-5}{8}\)

h) 1 và \(\dfrac{1}{6}\) - 3 và \(\dfrac{1}{3}\) =\(\dfrac{7}{6}\) -\(\dfrac{10}{3}\) = \(\dfrac{-13}{6}\)

i) \(\dfrac{-2}{5}\) . (-3) + \(\dfrac{3}{8}\) . \(\dfrac{4}{-10}\) =(\(\dfrac{-2}{5}\) .\(\dfrac{-4}{10}\)) + [(-3) . \(\dfrac{3}{8}\) 

                                     = \(\dfrac{4}{25}\) + \(\dfrac{-9}{8}\) = \(\dfrac{32}{200}\) + \(\dfrac{-225}{200}\)  = \(\dfrac{-193}{200}\)

j) \(\dfrac{-13}{17}\) + (\(\dfrac{13}{-21}\) + \(\dfrac{-4}{17}\) )

= ( \(\dfrac{-13}{17}\) + \(\dfrac{-4}{17}\) )+\(\dfrac{-13}{21}\) 

= -1+\(\dfrac{-13}{21}\)

= \(\dfrac{-21}{21}\) + \(\dfrac{-13}{21}\) = \(\dfrac{-34}{21}\)

_{Khôi nguyễn}

sao tính nổi:))

a) = 1/2

b) = 4/15

c) = 1/12

d) = 13/12

a) \(\frac{20}{16}-\frac{3}{4}=\frac{20}{16}-\frac{12}{16}=\frac{8}{16}=\frac{1}{2}\)

b) \(\frac{30}{45}-\frac{2}{5}=\frac{30}{45}-\frac{18}{45}=\frac{12}{45}=\frac{4}{15}\)

c) \(\frac{10}{12}-\frac{3}{4}=\frac{10}{12}-\frac{8}{12}=\frac{1}{12}\)

a) \(\frac{20}{16}-\frac{3}{4}=\frac{5}{4}-\frac{3}{4}=\frac{1}{2}\)

b) \(\frac{30}{45}-\frac{2}{5}=\frac{2}{3}-\frac{2}{5}=\frac{10}{15}-\frac{6}{15}=\frac{4}{15}\)

c) \(\frac{10}{12}-\frac{3}{4}=\frac{10}{12}-\frac{9}{12}=\frac{1}{12}\)

d) \(\frac{12}{9}-\frac{1}{4}=\frac{4}{3}-\frac{1}{4}=\frac{16}{12}-\frac{3}{12}=\frac{13}{12}\)

@muối

Bài 2: 

a: A=(12,87+14,13)+(-14,7-37,3)

=27-52=-25

b: B=-1/3+2/5-2/3-3/5+1/5

=-1

a,1/2

b,4/15

c,1/12

d,13/12

k mk nhé

\(\frac{20}{16}-\frac{3}{4}=\frac{5}{4}-\frac{3}{4}=\frac{2}{4}=\frac{1}{2}\)

\(\frac{30}{45}-\frac{2}{5}=\frac{2}{3}-\frac{2}{5}=\frac{10}{15}-\frac{6}{15}=\frac{4}{15}\)

\(\frac{10}{12}-\frac{3}{4}=\frac{10}{12}-\frac{9}{12}=\frac{1}{12}\)

\(\frac{12}{9}-\frac{1}{4}=\frac{4}{3}-\frac{1}{4}=\frac{16}{12}-\frac{3}{12}=\frac{13}{12}\)

Cách trình bày nha bạn !!!!

bài 3:

\(A=\dfrac{9}{1\cdot2}+\dfrac{9}{2\cdot3}+\dfrac{9}{3\cdot4}+...+\dfrac{9}{2021\cdot2022}\)

\(=9\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{2021\cdot2022}\right)\)

\(=9\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{2021}-\dfrac{1}{2022}\right)\)

\(=9\cdot\dfrac{2021}{2022}=\dfrac{6063}{674}\)

Bài 1:

a: \(\left(\dfrac{1}{2}+\dfrac{16}{30}\right)-\left(1+\dfrac{1}{30}\right)\)

\(=\dfrac{15+16}{30}-1-\dfrac{1}{30}\)

\(=\dfrac{30}{30}-1\)

=1-1

=0

b: \(\dfrac{-5}{11}\cdot\dfrac{4}{13}+\dfrac{-5}{11}\cdot\dfrac{9}{13}+3\dfrac{5}{11}\)

\(=-\dfrac{5}{11}\left(\dfrac{4}{13}+\dfrac{9}{13}\right)+3+\dfrac{5}{11}\)

\(=-\dfrac{5}{11}+3+\dfrac{5}{11}\)

=3

c: \(3^2-12\left(\dfrac{3}{4}-\dfrac{2}{3}\right)\)

\(=9-12\cdot\dfrac{9-8}{12}\)

=9-1

=8

a) \(\dfrac{3}{8}+\dfrac{7}{12}+\dfrac{10}{16}+\dfrac{10}{24}\)

\(=\dfrac{3}{8}+\dfrac{7}{12}+\dfrac{5}{8}+\dfrac{5}{12}\)

\(=\left(\dfrac{3}{8}+\dfrac{5}{8}\right)+\left(\dfrac{7}{12}+\dfrac{5}{12}\right)\)

\(=1+1\)

\(=2\)

b) \(\dfrac{4}{6}+\dfrac{7}{13}+\dfrac{17}{9}+\dfrac{19}{13}+\dfrac{1}{9}+\dfrac{14}{6}\)

\(=\dfrac{2}{3}+\dfrac{7}{13}+\dfrac{17}{9}+\dfrac{19}{13}+\dfrac{1}{9}+\dfrac{7}{3}\)

\(=\left(\dfrac{2}{3}+\dfrac{7}{3}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)+\left(\dfrac{17}{9}+\dfrac{1}{9}\right)\)

\(=3+2+2\)

\(=7\)

c) \(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}\)

\(=\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+\dfrac{1}{6\cdot7}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\)

\(=1-\dfrac{1}{7}\)

\(=\dfrac{6}{7}\)