\(\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\\ =\dfrac{4}{5}+\dfrac{2}{7}-\dfrac{7}{10}\\ =\dfrac{56}{70}+\dfrac{20}{70}-\dfrac{49}{70}\\ =\dfrac{27}{70}\\ 3,5-\left(-\dfrac{2}{7}\right)\\ =\dfrac{7}{2}+\dfrac{2}{7}\\ =\dfrac{49}{14}+\dfrac{4}{14}\\ =\dfrac{53}{14}\\ \left(-3\right).\left(-\dfrac{7}{12}\right)\\ =\dfrac{21}{12}\\ =\dfrac{7}{4}\)

1)\(3,5\cdot x+1,54\cdot3,5=15\)

    \(3,5\left(x+1,54\right)=15\)

                 \(x+1,54=\frac{15}{3,5}\)

                 \(x+1,54=\frac{30}{7}\)

                                \(x=\frac{30}{7}-1,54\)

                                 \(x=\frac{30}{7}-\frac{77}{50}\)

                               \(x=\frac{961}{350}\)

\(20+\frac{12}{x-2019}=32\)

             \(\frac{12}{x-2019}=32-20\)

              \(\frac{12}{x-2019}=12\)

               \(x-2019=\frac{12}{12}\)

              \(x-2019=1\)

                               \(x=1+2019\)

2)

\(\frac{3}{7}\cdot\frac{4}{13}+\frac{3}{7}\cdot\frac{9}{13}+5\frac{4}{7}\)

\(=\frac{3}{7}\cdot\frac{4}{13}+\frac{3}{7}\cdot\frac{9}{13}+13\cdot\frac{3}{7}\)

\(=\frac{3}{7}\left(\frac{4}{13}+\frac{9}{13}+13\right)\)

\(=\frac{3}{7}\cdot14\)

\(=6\)

3.5*(x-1.54)=15

x+1.54=15;3.5

x+1.54=4.28

x=4.28-1.54

x=2.74

chưa suy nghĩ

3,5×(x+1,54)=15

(x+1,54)=15:3,5

(x+1,54)=30/7

(x+77/50)=30/7

x=30/7-77/50

x=961/350

\(=\dfrac{1}{16}-\dfrac{7}{2}+\sqrt{7}=\dfrac{-55}{16}+\sqrt{7}\)

\(\left(-\dfrac{1}{4}\right)^2-3,5+\sqrt{7}\\ =\dfrac{1}{16}-3,5+\sqrt{7}\\ =-\dfrac{55}{16}+\sqrt{7}\\ =\dfrac{-55+16\sqrt{7}}{16}\)

= \(\dfrac{1}{16}-3,5+\)√7

= \(\dfrac{-55+16\sqrt{7}}{16}\)

A) -15,5 x 20,8 +2,5 x 9,2 -15,5 x 9,2 + 3,5 x 20,8

=-15,5 x 20,8 + 2,5 x 9,2 + -15,5 x 9,2 +3,5 x 20,8

=[20,8x(-15,5+3,5)]+[9,2x(2,5+-15,5)]

=[20,8x(-12)]+[9,2x(-13)]

=-249,6+-119,6

=-369,2

a) -369,2

b) -7

B)(-3/4+5/13):2/7-(9/4-8/13):2/7

=(-19/52-85/52):2/7

=-2:2/7

=-7

\(\left(\dfrac{7}{8}-\dfrac{3}{4}\right)\cdot\dfrac{1}{3}-\dfrac{2}{7}\cdot\left(3,5\right)^2\)
\(=\left(\dfrac{7}{8}-\dfrac{6}{8}\right)\cdot\dfrac{1}{3}-\dfrac{2}{7}\cdot\dfrac{49}{4}\)
\(=\dfrac{1}{8}\cdot\dfrac{1}{3}-\dfrac{7}{2}\)
\(=\dfrac{1}{24}-\dfrac{7}{2}\)
\(=\dfrac{1}{24}-\dfrac{84}{24}\)
\(=-\dfrac{83}{24}\)
#データネ

`(7/8-3/4)xx1/3-2/7xx(3,5)^2`

`=(7/8-6/8)xx1/3-2/7xx12,25`

`=1/8xx1/3-2/7xx12,25`

`=1/24-7/2`

`=1/24-84/24`

`=-83/24`

Bài làm:

\(3,5\times6\times7-\left(\frac{1}{2}+\frac{10}{4}\right)\)

\(=21\times7-3\)

\(=147-3\)

\(=144\)

Học tốt 

Bài làm

3,5 . 6 . 7 - ( 1/2 + 10/4 )

= 21 . 7 - ( 2/4 + 10/4 )

= 147 - 12/4

= 147 - 3

= 144 

3,5 . 6 . 7 - ( 1/2 + 10/4 )

= 21 . 7 - ( 2/4 + 10/4 )

= 147 - 12/4

= 147 - 3

= 144

Vậy ......

a,\(3:7+\left(-5:2\right)+\left(-3:5\right)\)

\(=\dfrac{3}{7}-\dfrac{5}{2}-\dfrac{3}{5}\)

\(=-\dfrac{187}{70}\)

b,\(-8:18-15:17\)

\(=-\dfrac{8}{18}-\dfrac{15}{17}\)

\(=-\dfrac{203}{153}\)

c,\(4:5-\left(-2:7\right)-7:10\)

\(=\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}\)

\(=\dfrac{27}{10}\)

d,\(3,5-\left(-2:7\right)\)

\(=3,5+\dfrac{2}{7}\)

\(=\dfrac{53}{14}\)