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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Đ/s : 2/3 nha bn

k cho mình nhé binn2011

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

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

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

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

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

=-1+1-5/8= -5/8

a. bằng77

b. bằng 13

lớp 2 đã học cái này rồi à

a. bằng77

b. bằng 13

ko xem dc de ban oi :/

2

a) Ta có: \(A=\dfrac{2}{7}+\dfrac{-3}{8}+\dfrac{11}{7}+\dfrac{1}{3}+\dfrac{1}{7}+\dfrac{5}{-8}\)

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

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

\(=1+\dfrac{1}{3}=\dfrac{4}{3}\)

b) Ta có: \(B=\dfrac{-3}{8}+\dfrac{12}{25}+\dfrac{5}{-8}+\dfrac{2}{-5}+\dfrac{13}{25}\)

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

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

\(=-\dfrac{2}{5}\)

Giải:

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

A= (2/7+11/7+1/7)+(-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

Chúc bạn học tốt!

a) Ta có: =(2/7+11/7+1/7)+(−3/8+−5/8)+1/3

=1+1/3=4/3

b) Ta có: =(−3/8+−5/8)+(12/25+13/25)+−2/5

=−2/5

1: =72/90+65/90=137/90

2: =24/56-77/56=-53/56

3: =-7/10+4/5=1/10

4: =15/100-4/100=11/100

5: =4/6-5/6=-1/6

6: =10/40-15/40-76/40=-81/40

7: =-9/10+7/18

=-81/90+35/90=-46/90=-23/45

8: =27/90-55/90=-28/90=-14/45

9: =36/60-50/60-35/60=-49/60

10: =-4/9+5/6-3/8

=-32/72+60/72-27/72

=1/72

\(1,\dfrac{4}{5}+\dfrac{13}{18}=\dfrac{72}{90}+\dfrac{65}{90}=\dfrac{137}{90}\)

\(2,\dfrac{3}{7}-\dfrac{11}{8}=\dfrac{24}{56}-\dfrac{77}{56}=\dfrac{-53}{56}\)

\(3,-\dfrac{7}{10}-\left(-\dfrac{4}{5}\right)=-\dfrac{7}{10}-\left(-\dfrac{8}{10}\right)=\dfrac{1}{10}\)

\(4,\dfrac{3}{20}-\dfrac{1}{25}=\dfrac{75}{500}-\dfrac{20}{500}=\dfrac{55}{500}=\dfrac{11}{100}\)

\(5,\dfrac{2}{3}-\dfrac{5}{6}=\dfrac{12}{18}-\dfrac{15}{18}=-\dfrac{3}{18}=-\dfrac{1}{6}\)

\(6,\dfrac{1}{4}+\left(-\dfrac{3}{8}\right)-\dfrac{19}{10}=\dfrac{8}{32}+\left(-\dfrac{12}{32}\right)-\dfrac{19}{10}=-\dfrac{4}{32}-\dfrac{19}{10}\)

\(=-\dfrac{1}{8}-\dfrac{19}{10}=-\dfrac{10}{80}-\dfrac{152}{80}=-\dfrac{162}{80}=-\dfrac{81}{40}\)

\(7,-\dfrac{9}{10}-\left(-\dfrac{7}{18}\right)=-\dfrac{162}{180}-\left(-\dfrac{70}{180}\right)=-\dfrac{92}{180}=-\dfrac{23}{45}\)

\(8,\dfrac{3}{10}-\dfrac{11}{18}=\dfrac{54}{180}-\dfrac{110}{180}=-\dfrac{56}{180}=-\dfrac{14}{45}\)

\(9,\dfrac{3}{5}-\dfrac{5}{6}+\left(-\dfrac{7}{12}\right)=\dfrac{18}{30}-\dfrac{25}{30}+\left(-\dfrac{7}{12}\right)=-\dfrac{7}{30}+\left(-\dfrac{7}{12}\right)\)

\(=-\dfrac{84}{360}+\left(-\dfrac{210}{360}\right)=-\dfrac{294}{360}=-\dfrac{49}{60}\)

\(10,-\dfrac{4}{9}-\dfrac{-5}{6}-\dfrac{3}{8}=-\dfrac{24}{54}-\dfrac{-45}{54}-\dfrac{3}{8}\)

\(=\dfrac{21}{54}-\dfrac{3}{8}=\dfrac{7}{18}-\dfrac{3}{8}=\dfrac{56}{144}-\dfrac{54}{144}=\dfrac{2}{144}=\dfrac{1}{72}\)

`@mt`

a, A= 1/5.6+1/6.7+1/7.8+...+1/24.25

=1/5-1/6+1/6-1/7+1/7-1/8+...+1/24-1/25

=1/5-1/25

=4/25

hok tốt k nha