A . \(3\cdot\dfrac{5}{4}-\dfrac{3^2}{4}=\dfrac{15}{4}-\dfrac{9}{4}=\dfrac{6}{4}=\dfrac{3}{2}\)

B, \(\dfrac{-3}{2}\cdot\left(\dfrac{7}{3}-\dfrac{5}{3}\cdot4\right)=\dfrac{-3}{2}\cdot\left(\dfrac{7}{3}-\dfrac{20}{3}\right)=\dfrac{-3}{2}\cdot\dfrac{-13}{2}=\dfrac{39}{4}\)

C , \(\dfrac{-21}{10}+\dfrac{21}{10}\cdot\dfrac{3}{4}-\dfrac{3}{4}=\dfrac{-84}{40}+\dfrac{63}{40}-\dfrac{30}{40}=\dfrac{-84+63-30}{40}=\dfrac{-51}{40}\)

D , \(\dfrac{-2}{3}+2\cdot\left(\dfrac{-2}{3}\right)\cdot3-3=\dfrac{-2}{3}\left(1+2\cdot3\right)-3=\dfrac{-2}{3}\cdot7-3=\dfrac{-14}{3}-\dfrac{9}{3}=-\dfrac{23}{3}\)

3 x 15 + 21 x 15 + 85 x 5

= 45 + 315 + 425

= 785

15 - 30 + 40 

= 25

21 + 19 - 50 + 10

= 0

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

\(=-\dfrac{1}{20}+2\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{12}\times\dfrac{3}{12}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=-\dfrac{9}{20}\)

\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)

\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)

\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)

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

\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)

\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)

\(=\dfrac{44}{20}-\dfrac{5}{20}\)

\(=\dfrac{39}{20}\)

\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)

\(=\dfrac{5}{12}\times\dfrac{1}{4}\)

\(=\dfrac{5}{48}\)

\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)

\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)

\(=\dfrac{6}{20}-\dfrac{15}{20}\)

\(=-\dfrac{9}{20}\)

\(\frac{18}{27}-\frac26\)

\(=\frac23-\frac13=\frac{2-1}{3}=\frac13\)

\(\frac{37}{12}-3=\frac{37}{12}-\frac{36}{12}=\frac{37-36}{12}=\frac{1}{12}\)

\(5-\frac{14}{3}=\frac{15}{3}-\frac{14}{3}=\frac{15-14}{3}=\frac13\)

\(\frac{10}{21}:\frac23=\frac{10}{21}\times\frac32=\frac{30}{42}=\frac57\)

\(\frac35:\frac34=\frac35\times\frac43=\frac33\times\frac45=\frac45\)

\(\frac25:\frac{3}{10}=\frac25\times\frac{10}{3}=\frac{20}{15}=\frac43\)

\(\frac38:\frac94=\frac38\times\frac49=\frac{12}{72}=\frac16\)

\(\frac{8}{21}:\frac47=\frac{8}{21}\times\frac74=\frac{7}{21}\times\frac84=\frac23\)

\(\frac85:\frac{15}{8}=\frac85\times\frac{8}{15}=\frac{64}{75}\)

đề bài đâu e

Đề bài tính 

c: \(=\dfrac{3}{2}\cdot1-1-20=\dfrac{3}{2}-21=\dfrac{-39}{2}\)

a, 5/-14. 7/-19=8/38

b, -15/4 .( 16/-25 )=12/5

c, 3/-10 .( -15/-2 )=

d, -5/7 . ( 21/-10 )=-9/4

e, 10/-3. (6/-5)==4

f, 21/-9 . ( -6/14 )=1

g, -10/9 . ( 36/20 )=-2

  \(\frac{27^3+9^{10}.2^4+4^2.81^5}{3^{10}+3^{21}.2^5}\)

=\(\frac{3^9+3^{20}.2^4+2^4.3^{20}}{3^{10}+3^{21}.2^5}\)

=\(\frac{3^{18}+2^3}{1}\)

= \(3^{18}+2^3\)

Hk tốt

a: \(C=\dfrac{-1}{2}:\dfrac{-2}{3}:\dfrac{-3}{4}\)

\(=\dfrac{-1}{2}\cdot\dfrac{3}{-2}\cdot\dfrac{4}{-3}\)

\(=-\dfrac{4}{4}=-1\)

b: \(D=\dfrac{-6}{5}:\dfrac{-5}{4}:\dfrac{-4}{3}\)

\(=-\dfrac{6}{5}\cdot\dfrac{4}{5}\cdot\dfrac{3}{4}\)

\(=\dfrac{-18}{25}\)

c: \(\dfrac{4}{20}+\dfrac{16}{42}+\dfrac{6}{15}+\dfrac{-3}{5}+\dfrac{2}{21}+\dfrac{-10}{21}+\dfrac{3}{20}\)

\(=\left(\dfrac{4}{20}+\dfrac{-3}{5}+\dfrac{6}{15}\right)+\left(\dfrac{16}{42}+\dfrac{2}{21}-\dfrac{10}{21}\right)+\dfrac{3}{20}\)

\(=\left(\dfrac{1}{5}-\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{8}{21}+\dfrac{2}{21}-\dfrac{10}{21}\right)+\dfrac{3}{20}\)

\(=\dfrac{3}{20}\)

d: \(\dfrac{42}{46}+\dfrac{250}{186}+\dfrac{-2121}{2323}+\dfrac{-125125}{143143}\)

\(=\dfrac{21}{23}+\dfrac{125}{93}+\dfrac{-21}{21}+\dfrac{-125}{143}\)

\(=\dfrac{125}{93}-\dfrac{125}{143}=\dfrac{6250}{13299}\)

Câu d, chỗ \(\dfrac{-21}{21}\) phải sửa thành \(\dfrac{-21}{23}\)

b: \(=2^5-1-9+21=53-10=43\)

c: \(=\dfrac{3}{2}-1-21=\dfrac{3}{2}-21=\dfrac{-39}{2}\)

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