\(3.\left(x-\frac{1}{5}\right)-7.\left(\frac{5}{14}-3\right)=20\)

\(3.\left(x-\frac{1}{5}\right)-7.\frac{-37}{14}=20\)

\(3.\left(x-\frac{1}{5}\right)-\frac{-37}{2}=20\)

\(3.\left(x-\frac{1}{5}\right)=20+\frac{-37}{2}\)

\(3.\left(x-\frac{1}{5}\right)=\frac{3}{2}\)

\(x-\frac{1}{5}=\frac{3}{2}:3\)

\(x-\frac{1}{5}=\frac{1}{2}\)

\(x=\frac{1}{2}+\frac{1}{5}\)

\(x=\frac{7}{10}\)

Giải tiếp đi bạn

\(\frac{2}{3}-\frac{1}{5}.\left(x-\frac{1}{4}\right)=\frac{3}{2}-\frac{1}{4}\)

\(\frac{2}{3}-\frac{1}{5}.\left(x-\frac{1}{4}\right)=\frac{5}{4}\)

\(\frac{1}{5}.\left(x-\frac{1}{4}\right)=\frac{2}{5}-\frac{5}{4}\)

\(\frac{1}{5}.\left(x-\frac{1}{4}\right)=\frac{-17}{20}\)

\(x-\frac{1}{4}=\frac{-17}{20}:\frac{1}{5}\)

\(x-\frac{1}{4}=\frac{-17}{4}\)

\(x=\frac{-17}{4}+\frac{1}{4}\)

\(x=-4\)

\(\frac{317.452-201}{451.317+116}=\frac{317.\left(451+1\right)-201}{451.317+116}=\frac{317.451+317-201}{451.317+116}\)\(=\frac{451.317+\left(317-201\right)}{451.317+116}=\frac{451.317+116}{451.317+116}\)\(=1\)

Vậy: \(\frac{317.452-201}{451.317+116}=1\)

[317 x 452 - 201][451x317+116]=[317x(451+1)-201][451x317+116]

=[317x451+317-201][451x317+116]

=[317x451-116][451x317-116]=1

nhớ nhé!

1 nha bạn

dễ mà 2/5 =6/7 em ak =)

cảm ơn nha

Câu hỏi của TRẦN THỊ BÍCH HỒNG - Toán lớp 7 - Học toán với OnlineMath

càng ngu

1 phan 4 

chi can tach mau ra de cho bang 1 

h cho minh nhe

Ta có: \(\frac{x-y}{3}=\frac{x+y}{13}=\frac{x-y+x+y}{16}=\frac{2x}{16}=\frac{x}{8}=\frac{25x}{200}=\frac{xy}{200}\)

Suy ra: \(25x=xy\Rightarrow y=25\)

Ta có: \(\frac{x-y}{3}=\frac{x+y}{13}\)

Suy ra: \(13x-13y=3x+3y\)

Thế y vào đẳng thức trên:

\(13x-325=3x+75\)

Suy ra: \(10x=325+75=400\Rightarrow x=40\)

Vậy ........

Bài 1:

ta có: 8⁷ - 2¹⁸ = (2³)⁷ - 2¹⁸ = 2²¹ - 2¹⁸ 

= 2¹⁷.(2⁴ -2) = 2¹⁷.14 chia hết cho 14

=> đpcm

Bài 1

8⁷-2¹⁸=2²¹-2¹⁸=2¹⁸.7\(⋮\)14

Bài 2

ab=c²<=>\(\frac{a}{c}=\frac{c}{b}=\frac{a}{b}=\frac{a^2+c^2}{b^2+c^2}\)(dãy tỉ số bằng nhau)

Bài 2:

ta có: \(ab=c^2\Rightarrow\frac{a}{c}=\frac{c}{b}\Rightarrow\frac{a}{c}\cdot\frac{c}{b}=\frac{a}{c}\cdot\frac{a}{c}=\frac{c}{b}\cdot\frac{c}{b}\)

                                                   \(\Rightarrow\frac{a}{b}=\frac{a^2}{c^2}=\frac{c^2}{b^2}\)

mà \(\frac{a^2}{c^2}=\frac{c^2}{b^2}=\frac{a^2+c^2}{c^2+b^2}\)

=> đpcm

Đặt X=phép tính trên

Ta có X=X x 1/2 :1/2

X=(1/6+1/12+...+1/6480):1/2

X=(1/2x3+1/3x4+...+1/80x81):1/2

X=(1/2-1/3+1/3-1/4+...+1/80-1/81):1/2

X=(1/2-1/81):1/2

Đến đây bạn tự tính nhé!!!

Đặt: A=...

\(\frac{A}{2}=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{6480}\)

\(\frac{A}{2}=\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}+...+\frac{1}{80x81}\)

\(\frac{A}{2}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{80}-\frac{1}{81}\)

\(\frac{A}{2}=\frac{1}{2}-\frac{1}{81}=\frac{79}{162}\) => A=\(\frac{79}{81}\)

Sửa đề nha :

\(\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+...+\frac{1}{2015\cdot2017}\)

\(=\frac{1}{2}\cdot\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2015}-\frac{1}{2017}\right)\)

\(=\frac{1}{2}\cdot\left(1-\frac{1}{2017}\right)\)

\(=\frac{1}{2}\cdot\frac{2016}{2017}=\frac{1008}{2017}\)

\(\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{2016.2017}\)

\(=\frac{1}{2}\left[\left[\frac{1}{1}-\frac{1}{3}\right]+\left[\frac{1}{3}-\frac{1}{5}\right]+...+\left[\frac{1}{2016}-\frac{1}{2017}\right]\right]\)

= \(=\frac{1}{2}\left[1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2016}-\frac{1}{2017}\right]\)

\(=\frac{1}{2}.\left[1-\frac{1}{2017}\right]\)

= 1/2. 2016 / 2017 = 1008/2017

AI ^{THẤY ĐÚNG}  ỦNG HỘ   NHA

thực sự mik ko làm được nhưng chúc bn thi tốt và có kq cao nha