a)15/34-8/21+19/34-34/21

 =(15/34+19/34)+(-8/21-34/21)

= 34/34+(-42/21)

=1+(-2)

=-1

đề tự ghi lại nha 

=\(\left(\frac{15}{34}+\frac{19}{34}\right)+\left(\frac{-8}{21}-\frac{34}{21}\right)\)

=\(\frac{34}{34}+\frac{-42}{21}\)

=\(1+\left(-2\right)\)

=\(-1\)

C

A

C nhé Khi ko tính số 0 trên dãy số trên thì ta có quy luật tổng hai số đằng sau sẽ bằng số ở phía trước (VD 1+2=3;3+2=5;3+5=8;8+5=13;...) mình chúc bạn học tốt nhé

\(\dfrac{15}{34}+\dfrac{7}{21}+\dfrac{19}{34}-1\dfrac{7}{21}+\dfrac{2}{5}=\left(\dfrac{15}{34}+\dfrac{19}{34}\right)+\left(\dfrac{7}{21}-\dfrac{4}{3}\right)+\dfrac{2}{5}=1+\left(-1\right)+\dfrac{2}{5}=0+\dfrac{2}{5}=\dfrac{2}{5}\)

\(\dfrac{15}{34}+\dfrac{7}{21}+\dfrac{19}{34}-\dfrac{3}{1}+\dfrac{7}{21}+2\)

\(=\left(\dfrac{15}{34}+\dfrac{19}{34}\right)+\left(\dfrac{7}{21}+\dfrac{7}{21}\right)-\left(3-2\right)\)

\(=1-1+\dfrac{14}{21}\)

\(=\dfrac{14}{21}\)

\(\dfrac{15}{34}+\dfrac{7}{21}+\dfrac{19}{34}-3+\dfrac{7}{21}+2\)

= \(\dfrac{15}{34}+\dfrac{19}{34}+\dfrac{7}{21}+\dfrac{7}{21}-3+2\)

= \(\left(\dfrac{15}{34}+\dfrac{19}{34}\right)+\left(\dfrac{7}{21}+\dfrac{7}{21}\right)-\left(3-2\right)\)

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

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

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

GOOD LUCK!

a) \(...=-\dfrac{12}{46}-\dfrac{15}{21}+\dfrac{3}{7}-\dfrac{7}{23}\)

\(=-\dfrac{12}{46}-\dfrac{7}{23}-\dfrac{15}{21}+\dfrac{3}{7}\)

\(=-\dfrac{6}{23}-\dfrac{7}{23}-\dfrac{5}{7}+\dfrac{3}{7}\)

\(=-\dfrac{13}{23}-\dfrac{2}{7}\)

\(=-\dfrac{13.7}{23.7}-\dfrac{2.23}{23.7}\)

\(=-\dfrac{91}{161}-\dfrac{46}{161}=-\dfrac{137}{161}\)

b) \(...=-21+\dfrac{7}{9}-\dfrac{3}{17}+\dfrac{25}{9}\)

\(=-21-\dfrac{3}{17}+\dfrac{7}{9}+\dfrac{25}{9}\)

\(=-21-\dfrac{3}{17}+\dfrac{32}{9}\)

\(=-\dfrac{3213}{153}-\dfrac{27}{153}+\dfrac{544}{153}=-\dfrac{2696}{153}\)

=15/34+19/34+1/3-4/3

=1-1

=0

=(15/34+19/34)+1/3-4/3
=1-1
=0

\(\dfrac{15}{34}+\dfrac{7}{21}+\dfrac{19}{34}-\dfrac{32}{17}+\dfrac{2}{3}\) 

\(=\left(\dfrac{15}{34}+\dfrac{19}{34}\right)+\dfrac{7}{21}+\dfrac{-32}{17}+\dfrac{2}{3}\) 

\(=1+\dfrac{1}{3}+\dfrac{-32}{17}+\dfrac{2}{3}\) 

\(=1+\left(\dfrac{1}{3}+\dfrac{2}{3}\right)+\dfrac{-32}{17}\) 

\(=1+1+\dfrac{-32}{17}\) 

\(2+\dfrac{-32}{17}=\dfrac{2}{17}\)

`15/34+7/21+9/34-1 15/17+2/3`

`=(15/34+9/34)+(7/21+2/3)-32/17`

`=12/17+1-32/17`

`=(12/17-32/17)+1`

`=-20/17+1`

`=-3/17`

\(\dfrac{15}{34}+\dfrac{7}{21}+\dfrac{9}{34}-1\dfrac{15}{17}+\dfrac{2}{3}\)
\(=\left(\dfrac{15}{34}+\dfrac{9}{34}-\dfrac{32}{17}\right)+\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)
\(=-\dfrac{25}{17}+1=-\dfrac{8}{17}\)