13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11

= 13/19 x (23/11 - 8/11 - 4/11)

= 13/19 x 1

= 13/19

\(\dfrac{13}{19}\times\dfrac{23}{11}-\dfrac{13}{19}\times\dfrac{8}{11}-\dfrac{13}{19}\times\dfrac{4}{11}\\ =\dfrac{13}{19}\times\left(\dfrac{23}{11}-\dfrac{8}{11}-\dfrac{4}{11}\right)\\ =\dfrac{13}{19}\times1=\dfrac{13}{19}\)

câu b, 20/5x7 + 20/7x9 + 20/ 9 x11 + ..... 20 / 33 x35

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)=\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}=2+\frac{8}{13}\)

\(=\frac{26}{13}+\frac{8}{13}=\frac{34}{13}\)

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)\)

\(=\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}\)

\(=2+\frac{8}{13}\)

\(=\frac{26}{13}+\frac{8}{13}=\frac{34}{13}\)

 bài làm rồi đi chép lại : )))?

\(\frac{13}{19}\times\frac{23}{11}-\frac{13}{19}\times\frac{8}{11}-\frac{13}{19}\times\frac{4}{11}\)

\(=\frac{13}{19}\times\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}\times1\)

\(=\frac{13}{19}\)

13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11

= 13/19 x (23/11 - 8/11 - 4/11)

= 13/19 x 1

= 13/19

\(\frac{13}{19}.\frac{23}{11}-\frac{13}{19}.\frac{8}{11}-\frac{13}{19}.\frac{4}{11}\)

\(=\frac{13}{19}.\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}.\frac{11}{11}\)

\(=\frac{13}{19}.1\)

\(=\frac{13}{19}\)

19/11 + ( 8/13 + 3/11 )

=( 19/11+3/11 )+8/13

=2+8/13

=26/13+8/13

=34/13

19/11+(8/13+3/11)

=(9/11+3/11)+8/13=2+8/13=34/13

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)\)

= \(\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)

= \(\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}\)

= 2 + \(\frac{8}{13}\)

= \(\frac{34}{13}\)

k mình nhé mình trả lời nhanh nhất , đầy đủ nhất và đúng nhất

19/11+{8/13+3/11}

={19/11+3/11}+8/13

=22/11+8/13

=2+8/13

=34/13

mk cũng không chắc nữa

chúc bạn học giỏi

^_^

1976

16/9

34/13

1976

16/9

34/13

1976

16/9

34/13

nhiều thế

sfdhg 

a) ( 2/5 + 3/5) + 7/8

= 5/5 +7/8

= 1+ 7/8

=15/8 ( tính lại hộ mk nha, sợ ko đúng)

b)( 19/11 + 3/11 ) + 5/13

= 22/11 +5/13

= 2 + 5/13

= ...( bn tính nốt nha, vì mk ko có nháp ở đây )

k nha!!!

a) (2/5 + 7/8) + 3/5

= 2/5 + 7/8 + 3/5

= (2/5 + 3/5) + 7/8

= 1 + 7/8

= \(1\frac{7}{8}\)

b) 19/11 + (5/13 + 3/11)

= 19/11 + 5/13 + 3/11

= (19/11 + 3/11) + 5/13

= 2 + 5/13

= \(2\frac{5}{13}\)

\(a,\left(\frac{2}{5}+\frac{7}{8}\right)+\frac{3}{5}\)

\(=\frac{2}{5}+\frac{7}{8}+\frac{3}{5}\)

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

\(=1+\frac{7}{8}\)

\(=\frac{15}{8}\)

\(b,\frac{19}{11}+\left(\frac{5}{13}+\frac{3}{11}\right)\)

\(=\frac{19}{11}+\frac{5}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{5}{13}\)

\(=2+\frac{5}{13}\)

\(=\frac{31}{13}\)

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

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

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

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

\(=\frac{5}{5}+\frac{22}{11}+\frac{26}{13}\)

\(=1+2+2=5\)

Số số hạng là 19-11+1=9(số)

Tổng là: 10x9=90

=(11+19)+(12+18)+(13+17)+(14+16)+15

=30+30+30+30+15

=135

90