A=2/7+-3/8+11/7+1/3+1/7+5/-8

A=(2/7 + 1/7 + 11/7) + (-3/8 + 5/-8) + 1/3

A=2 + (-1) + 1/3

A=1 + 1/3

A=4/3

B=-3/8+12/25+5/-8+2/-5+13/25

B=(-3/8 + 5/-8) + (12/25 + 13/25) + 2/-5

B=-1 + 1 + 2/-5

B=-2/5

B=4*13/9*3-4/3*40/9

B=4/3*13/9-4/3*40/9

B=4/3*(13/9-40/9)

B=4/3*(-27)/9

B=4*(-3)/9

B=-4

A=6/7 + 1/7.(2/7+5/7)

A=6/7 + 1/7.7/7=6/7+1/7.1

A=6/7+1/7=7/7=1

M=8/3*2/5*3/8*10*19/2

M=(8/3*3/8)*(2/5*10)*19/2

M=1*4*19/2

M=28

A = 2/7 + 11/7 -3/8 - 5/8 + 1/3 + 1/5 = 13/11 - 1 + 8/15

A = 2/11 + 8/15 = 118/125

B = - 3/17 + 3/17 + 2/13 = 2/13

C = - 3/8 - 5/8 + 12/15 = 1 - 12/15

C = - 1/5 

\(A=\frac{2}{7}+\left(-\frac{3}{8}\right)+\frac{11}{7}+\frac{1}{3}+\frac{1}{7}+\left(-\frac{5}{8}\right)\)

\(=\left(\frac{2}{7}+\frac{11}{7}+\frac{1}{7}\right)+\left(-\frac{3}{8}-\frac{5}{8}\right)+\frac{1}{3}\)

\(=2-1+\frac{1}{3}\)

\(=1+\frac{1}{3}\)

\(=\frac{4}{3}\)

\(B=-\frac{3}{17}+\left(\frac{2}{3}+\frac{3}{17}\right)\)

\(=-\frac{3}{17}+\frac{2}{3}+\frac{3}{17}\)

\(=\left(-\frac{3}{17}+\frac{3}{17}\right)+\frac{2}{3}\)

\(=0+\frac{2}{3}\)

\(=\frac{2}{3}\)

\(C=\frac{3}{8}+\frac{12}{25}+\frac{5}{-8}+\frac{2}{-5}+\frac{13}{25}\)

\(=\left(\frac{3}{8}-\frac{5}{8}\right)+\left(\frac{12}{25}+\frac{13}{25}\right)-\frac{2}{5}\)

\(=-\frac{1}{4}+1-\frac{2}{3}\)

\(=\frac{1}{12}\)

Đ/s : 2/3 nha bn

k cho mình nhé binn2011

A=(2+3+...+13)-(1+2+...+12)=2+3+...+13-1-2-...-12=(13-1)+(2-2)+(3-3)+...+(12-12)=12

12 nha cậu .

2: \(=\dfrac{-2}{75}+\dfrac{5}{39}=\dfrac{33}{325}\)

3: \(=\dfrac{6}{11}\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{6}{11}\)

4: \(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}-1\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)

5: \(=\dfrac{2}{7}\left(\dfrac{4}{23}-\dfrac{27}{23}+1\right)=0\)

6: \(=\dfrac{3}{8}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{11}{8}=\dfrac{3}{8}+\dfrac{11}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)