Ta có: \(-\frac59\cdot\frac{13}{28}-\frac{13}{28}\cdot\frac49\)

\(=-\frac{13}{28}\left(\frac59+\frac49\right)\)

\(=-\frac{13}{28}\cdot\frac99=-\frac{13}{28}\)

-5/9 . 13/28 - 13/28 . 4/9

= 13/28 . (-5/9 - 4/9)

= 13/28 . (-1)

= -13/28

`-5/9 xx 13/28 - 13/28 xx 4/9`

`= 13/28 xx ((-5)/9 - 4/9)`

`= 13/28 xx (-1)`

`= -13/28`

\(A=\frac{13}{28}\left(-\frac{5}{9}-\frac{4}{9}\right)=\frac{13}{28}\left(-\frac{9}{9}\right)=\frac{13}{28}\left(-1\right)\)

=> \(A=-\frac{13}{28}\)

A= -5/9x 13/28- 13/28x 4/9

  =13/28x (-5/9- 4/9)

  =13/28x (-1)

  =-13/28

a)

 \(\frac{{28}}{9} \cdot 0,7 + \frac{{28}}{9} \cdot 0,5 = \frac{{28}}{9}.\left( {0,7 + 0,5} \right)\)

b)

\(\begin{array}{l}\frac{{36}}{{13}}:4 + \frac{{36}}{{13}}:9\\ = \frac{{36}}{{13}}.\frac{1}{4} + \frac{{36}}{{13}}.\frac{1}{9}\\ = \frac{{36}}{{13}}.\left( {\frac{1}{4} + \frac{1}{9}} \right)\\ = \frac{{36}}{{13}}.\frac{{13}}{{36}} = 1\end{array}\)

 \(\begin{array}{l}\frac{{36}}{{13}}:(4 + 9)\\ = \frac{{36}}{{13}}:13\\ = \frac{{36}}{{13}}.\frac{1}{{13}}\\ = \frac{{36}}{{169}}\end{array}\)

Suy ra \(\frac{{36}}{{13}}:4 + \frac{{36}}{{13}}:9\) \( \ne \) \(\frac{{36}}{{13}}:(4 + 9)\).

\(\frac{-5}{9}.\frac{13}{28}-\frac{13}{28}.\frac{4}{9}\)

\(=\frac{13}{28}.\left(\frac{-5}{9}-\frac{4}{9}\right)\)

\(=\frac{13}{28}.\left(-1\right)\)

\(=\frac{-13}{28}\)

=13/28.(-5/9-4/9)

=13/28.(-1)

=-13/28

\(\frac{-5}{9}.\frac{13}{28}-\frac{13}{28}.\frac{4}{9}\)

= \(\frac{13}{28}.\left(\frac{-5}{9}-\frac{4}{9}\right)\)

= \(\frac{13}{28}.\left(-1\right)=\frac{-13}{28}\)

~~~

#Sunrise

-13/28

Phương pháp giải:

- Thực hiện phép tính nhân hoặc chia rồi cộng hoặc trừ với số còn lại. 

- Trình bày lần lượt theo thứ tự các phép tính vừa tính.

Lời giải chi tiết:

5 × 3 + 5 = 15 + 5 = 20

28 : 4 + 13 = 7 + 13 = 20

4 × 9 − 16 = 36 − 16 = 20

a, A = ( 1/3 + 12/67 + 13/41 ) - ( 79/67 - 28/41 )

A = (\(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\)) - (\(\frac{79}{67}\) - \(\frac{28}{41}\))

A = \(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\) - \(\frac{79}{67}\) + \(\frac{28}{41}\)

A = - (\(\frac{79}{67}-\frac{12}{67}\)) + (\(\frac{13}{41}\) + \(\frac{28}{41}\))

A = - 1 + 1 + \(\frac13\)

A = 0 + \(\frac13\)

A = \(\frac13\)

b, B = 3/4×7 + 3/7×10 + 3/10×13 + ......+ 3/73×76

B = \(\frac{3}{4\times7}\) + \(\frac{3}{7\times10}\) + \(\frac{3}{10\times13}\) + ... + \(\frac{3}{73\times76}\)

B = \(\frac14-\frac17\) + \(\frac17-\frac{1}{10}\) + ... + \(\frac{1}{73}-\frac{1}{76}\)

B = \(\frac14\) - \(\frac{1}{76}\)

B = \(\frac{19}{76}-\) \(\frac{1}{76}\)

B = \(\frac{18}{76}\)

B = \(\frac{9}{38}\)