a: \(\dfrac{-11}{18}+\dfrac{12}{29}+\dfrac{-7}{18}+\dfrac{2020}{2021}+\dfrac{17}{29}\)

=(-11/18-7/18)+(12/29+17/29)+2020/2021

=2020/2021

b: \(\dfrac{-2}{3}\cdot\dfrac{4}{9}+\dfrac{5}{9}\cdot\dfrac{-2}{3}+\dfrac{4}{3}\)

=-2/3+4/3=2/3

a) https://hoc247.net/hoi-dap/toan-7/thuc-hien-phep-tinh-5-5-27-7-23-0-5-5-27-16-23-faq218258.html

b) https://hoidap247.com/cau-hoi/1507941

b) \(\dfrac{10^9.49^4}{14^8.25^5}=\dfrac{\left(2.5\right)^9.\left(7^2\right)^4}{\left(7.2\right)^8.\left(5^2\right)^5}=\dfrac{2^9.5^9.7^6}{7^8.2^8.5^{10}}=\dfrac{2}{7.7.5}=\dfrac{2}{245}\)

\(a,=\left(\dfrac{140}{27}+\dfrac{1}{2}\cdot\dfrac{5}{27}\right)+\left(\dfrac{7}{23}+\dfrac{16}{23}\right)\\ =\left(\dfrac{140}{27}+\dfrac{5}{54}\right)+1=\dfrac{285}{54}+1=\dfrac{339}{54}=\dfrac{113}{18}\\ b,=\dfrac{2^9\cdot5^9\cdot7^8}{7^8\cdot2^8\cdot5^{10}}=\dfrac{2}{5}\)

a) = 30

b) = 5

c) = 70

a)12+24+35-2-14-25=30

b)1-2+3-4+5-6+7-8+9=5

c)25-12-3+24+36=70

a) = 30

b) = 5

c) = 70

Số số hạng là:

(2017 - 4) : 3 + 1 = 672

Tổng: (2017 + 4) x 672 : 2 = 679056

Số số hạng: (98 - 10) : 2 + 1 = 45

Tổng: (98 + 10) x 45 : 2 = 2430

OK

Cách 1 : \(\left(\frac{1}{4}-\frac{1}{7}\right)\times\frac{1}{3}\)

\(=\frac{3}{28}\times\frac{1}{3}\)

\(=\frac{1}{28}\)

Cách 2:\(\left(\frac{1}{4}-\frac{1}{7}\right)\times\frac{1}{3}\)

\(=\frac{1}{4}\times\frac{1}{3}-\frac{1}{7}\times\frac{1}{3}\)

\(=\frac{1}{12}-\frac{1}{21}\)

\(=\frac{1}{28}\)

cách 1:

( 1/4 - 1/7) x 1/3 = 1/28

cách 2:

( 1/4 - 1/7) x 1/3 = 1/4 x 1/3 - 1/7 x 1/3

                        = 1/12 - 1/21

                        = 1/18

( 1/4 - 1/7 ) x 1/3 =

cách 1 : ( 1/4 - 1/7 ) x 1/3 = 3/28 x 1/3 = 1/28

cách 2 : ( 1/4 - 1/7 ) x 1/3 = 1/4 x 1/3 - 1/7 x 1/3 = 1/12 - 1/21 = 1/28

ai thấy đúng thì tk mk nha 

ê tk cho mình đi đang thiếu điểm 

xin vui lòng

alo anh em