\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

\(=\dfrac{2}{5}\times\left(\dfrac{1}{7}+\dfrac{2}{7}\right)\)

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

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(x+\dfrac{1}{6}=\dfrac{3}{4}\)

\(x=\dfrac{9}{12}-\dfrac{2}{12}\)

\(x=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}-\dfrac{1}{2020}\)

\(x=\dfrac{1010}{2020}-\dfrac{1}{2020}\)

\(x=\dfrac{1009}{2020}\)

\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

\(=\dfrac{2}{5}\times\left(\dfrac{1}{7}+\dfrac{2}{7}\right)\)

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

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}-x\)

\(\Rightarrow\dfrac{3}{4}-x=\dfrac{1}{6}\)

\(\Rightarrow x=\dfrac{3}{4}-\dfrac{1}{6}=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1\times2\times3\times4\times...\times2019}{2\times3\times4\times5\times...\times2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{1}{2}-\dfrac{1}{2020}=\dfrac{1009}{2020}\)

a. \(2^4\cdot3^2\)
b. \(x^5\)

c. \(3^4\cdot4^2\cdot2^2\)

:((

À quên mọi người tính nhanh nhé !

a) \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}\)

\(=1-\frac{1}{4}\)

\(=\frac{3}{4}\)

b) \(\frac{4}{7}\times\frac{8}{9}+\frac{4}{7}\times\frac{1}{9}\)

\(=\frac{4}{7}\times\left(\frac{8}{9}+\frac{1}{9}\right)\)

\(=\frac{4}{7}\times1\)

\(=\frac{4}{7}\)

c) \(\frac{13}{6}\times\frac{3}{8}-\frac{3}{8}\times\frac{7}{6}\)

\(=\frac{3}{8}\times\left(\frac{13}{6}-\frac{7}{6}\right)\)

\(=\frac{3}{8}\times1\)

\(=\frac{3}{8}\)

d) \(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)

\(=1-\frac{1}{10}\)

\(=\frac{9}{10}\)

a) Bạn tự làm :V

b) \(\frac{4}{7}\times\frac{8}{9}+\frac{4}{7}\times\frac{1}{9}\)

\(=\frac{4}{7}\times\left(\frac{8}{9}+\frac{1}{9}\right)\)

\(=\frac{4}{7}\times1\)

\(=\frac{4}{7}\)

c) \(\frac{13}{6}\times\frac{3}{8}-\frac{3}{8}\times\frac{7}{6}\)

\(=\frac{3}{8}\times\left(\frac{13}{6}-\frac{7}{6}\right)\)

\(=\frac{3}{8}\times1\)

\(=\frac{3}{8}\)

d) Bạn tự làm :v

3 nhân 2/3 bao nhiêu

1800 nha

đúng k nhỉ

\(1+2+3+4+5\times1\times2\times3\times4\times5\)

=\(1+2+3+4+\left(5\times1\times2\times3\times4\times5\right)\)

\(=10+600\)

\(=610\)

ban sai rùi nha

bang 450

1)1/9 x 3^x = 2187:81=27

            3^x=27:1/9=243=3⁵

            =>x=5

\(\frac{1}{9}.3^4.3^x=3^7\)

\(\Leftrightarrow3^x=3^7:\frac{1}{9}:3^4=243\)

\(\Leftrightarrow3^x=3^5\)

\(\Leftrightarrow x=5\)

Nhân chia trước cộng trừ sau.

 Chúc bạn học tốt!

Bn làm nhân chia trước cộng trừ sau nhé.

áp dụng công thức bn nhé

chúc bn hộc tốt

a) 2629x21-2526=52683 b) 42567+12312:24=43080 c) 115938:57-57=1977 d) 2/3+5/2-3/4=29/12 e)......tự làm

\(\frac{1}{1}\)x 2 x 3 + \(\frac{1}{2}\)x 3 x 4 + \(\frac{1}{3}\)x 4 x 5 + \(\frac{1}{4}\)x 5 x 6

= 1 x 2 + \(\frac{1}{2}\)+ \(\frac{1}{3}\)+ \(\frac{1}{4}\)x 6

= 2 +\(\frac{1}{2}\)+ \(\frac{1}{3}\)+ 1, 5

=

\(A=\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+\dfrac{1}{3.4.5}+...+\dfrac{1}{18.19.20}\)

\(2A=\dfrac{3-1}{1.2.3}+\dfrac{4-2}{2.3.4}+\dfrac{5-3}{3.4.5}+...+\dfrac{20-18}{18.19.20}=\)

\(=\dfrac{1}{1.2}-\dfrac{1}{2.3}+\dfrac{1}{2.3}-\dfrac{1}{3.4}+\dfrac{1}{3.4}-\dfrac{1}{4.5}+...+\dfrac{1}{18.19}-\dfrac{1}{19.20}=\dfrac{1}{2}-\dfrac{1}{19.20}\)

\(\Rightarrow A=\left(\dfrac{1}{2}-\dfrac{1}{19.20}\right):2\)