\(\dfrac{-5}{7}\cdot\dfrac{3}{13}-\dfrac{5}{7}\cdot\dfrac{10}{13}+1\dfrac{5}{7}=\dfrac{5}{7}\cdot\dfrac{-3}{13}-\dfrac{5}{7}\cdot\dfrac{10}{13}+\dfrac{12}{7}\cdot1=\dfrac{5}{7}\cdot\left(\dfrac{-3}{13}-\dfrac{10}{13}\right)+\dfrac{12}{7}=\dfrac{5}{7}-1+\dfrac{12}{7}=-\dfrac{5}{7}+\dfrac{12}{7}=\dfrac{7}{7}=1\)

=-5/7(3/13+10/13)+12/7

=-5/7+12/7=1

\(\dfrac{8}{13}+\dfrac{4}{9}+\dfrac{1}{3}+\dfrac{5}{13}+3\)

\(=1+\dfrac{7}{9}+3\)

\(=4+\dfrac{7}{9}=\dfrac{43}{9}\)

cảm ơn bạn nhìu nhưng...

còn phần b thì sao bạn

(1/5+4/5)+(5/7+4/7)+(1/8+13/8)

=1+9/7+7/4

=28/28+36/28+49/28

=113/28

\(\frac{1}{5}+\frac{5}{7}+\frac{1}{8}+\frac{13}{8}+\frac{4}{5}+\frac{4}{7}\)

\(=\left(\frac{1}{5}+\frac{4}{5}\right)+\left(\frac{5}{7}+\frac{4}{7}\right)+\left(\frac{1}{8}+\frac{13}{8}\right)\)

\(=1+\frac{9}{7}+\frac{7}{4}\)

\(=\frac{28}{28}+\frac{36}{28}+\frac{49}{28}\)

\(=\frac{113}{28}\)

Ai k mik mik k lại

`13/7+5/6+1/7+7/6`

`=(13/7+1/7)+(5/6+7/6)`

`=14/7+12/6`

`=2+2`

`=4`

\(\dfrac{13}{7}+\dfrac{5}{6}+\dfrac{1}{7}+\dfrac{7}{6}\)
\(=\left(\dfrac{13}{7}+\dfrac{1}{7}\right)+\left(\dfrac{5}{6}+\dfrac{7}{6}\right)\)
\(=2+2\)
\(=4\)

\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)

`7/13+5/9+6/13+5/9`

`=(7/13+6/13)+(5/9+5/9)`

`=13/13+10/9`

`=1+10/9`

`=9/9+10/9`

`=19/9`

19/9

vvvvvvvvvvvvvvvv

8/13+4/9+1/3+5/13+3=

(8/13+5/13)+(4/9+3/9)+3=

1+7/9+3=4 7/9

8/5x4/7+4/7x2/5=

4/7x(8/5+2/5)

=4/7x2=8/7

\(\frac{3}{5}+\frac{6}{11}+\frac{7}{13}+\frac{2}{5}+\frac{16}{11}+\frac{19}{13}=\left(\frac{3}{5}+\frac{2}{5}\right)\left(\frac{6}{11}+\frac{16}{11}\right)\left(\frac{7}{13}+\frac{19}{13}\right)=1+2+2=5\)

Ta có:3/5+2/5=5/5=1; 6/11+16/11=22/11=2; 7/13+19/13=26/13=2

kết quả là 1+2+2=5

\(\frac{12}{13}+\frac{2}{7}+\frac{8}{13}+\frac{5}{7}\)

\(=\frac{12}{13}+\frac{8}{13}+\frac{5}{7}+\frac{2}{7}\)

\(=\frac{20}{13}+1\)

\(=\frac{33}{13}\)

\(\frac{12}{13}+\frac{2}{7}+\frac{8}{13}+\frac{5}{7}\)

\(=\left(\frac{12}{13}+\frac{8}{13}\right)+\left(\frac{2}{7}+\frac{5}{7}\right)\)

\(=\frac{20}{13}+1\)

\(=\frac{33}{13}\)