13/21 + x = 2/3
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Khách
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F
23 tháng 1 2020
Bài giải
a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)
\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)
b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)
\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)
c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)
d, \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)
\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)
\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)
\(=1+1+1\)
\(=3\)
e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)
\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)
\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)
\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)
\(=1+1+1\)
\(=3\)
M
23 tháng 1 2020
a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)
\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)
b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)
\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)
c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)
d, \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)
\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)
\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)
\(=1+1+1\)
\(=3\)
e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)
\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)
\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)
\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)
\(=1+1+1\)
\(=3\)
24 tháng 2 2022
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26+12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5+56}{64}=\dfrac{61}{64}\)
24 tháng 2 2022
\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26}{81}+\dfrac{4\times3}{27\times3}=\dfrac{26}{81}+\dfrac{12}{81}=\dfrac{38}{81}\)
\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5}{64}+\dfrac{7\times8}{8\times8}=\dfrac{5}{64}+\dfrac{56}{64}=\dfrac{61}{64}\)
NT
3
MN
7 tháng 3 2018
a) \(\frac{3}{4}\times\frac{1}{2}\times2\)
C1: \(=\frac{3}{8}\times2=\frac{3}{4}\)
C2: \(=\frac{3}{4}\times1=\frac{3}{4}\)
b) \(\left[\frac{3}{4}+\frac{1}{2}\right]\times\frac{5}{7}\)
C1: \(=\frac{5}{4}\times\frac{5}{7}=\frac{25}{28}\)
C2: \(=\frac{3}{4}\times\frac{5}{7}+\frac{1}{2}\times\frac{5}{7}=\frac{15}{28}+\frac{5}{14}=\frac{25}{28}\)
7 tháng 3 2018
a/\(\frac{3}{4}\cdot\frac{1}{2}\cdot2=\frac{6}{8}\cdot2=\frac{12}{8}=\frac{3}{2}\)
\(\frac{3}{4}\cdot\frac{1}{2}\cdot2=\frac{3}{4}\cdot\frac{2}{2}=\frac{3}{4}\cdot1=\frac{3}{4}\)
b/\(\left(\frac{3}{4}+\frac{1}{2}\right)\cdot\frac{5}{7}=\frac{5}{4}\cdot\frac{5}{7}=\frac{25}{28}\)
\(\left(\frac{3}{4}+\frac{1}{2}\right)\cdot\frac{5}{7}=\frac{3}{4}\cdot\frac{5}{7}+\frac{1}{2}\cdot\frac{5}{7}=\frac{15}{28}+\frac{5}{14}=\frac{15}{28}+\frac{10}{28}=\frac{25}{28}\)
c/\(\frac{5}{7}\cdot\frac{13}{21}+\frac{2}{7}\cdot\frac{13}{21}=\frac{65}{147}+\frac{26}{147}=\frac{91}{147}=\frac{13}{21}\)
\(\frac{5}{7}\cdot\frac{13}{21}+\frac{2}{7}\cdot\frac{13}{21}=\left(\frac{5}{7}+\frac{2}{7}\right)\cdot\frac{13}{21}=1\cdot\frac{13}{21}=\frac{13}{21}\)
Học tốt @#_#@
14 tháng 8 2023
a \(\dfrac{1}{x-y}+\dfrac{2}{x+y}+\dfrac{3x}{y^2-x^2}\)
\(=\dfrac{x+y+2x-2y-3x}{\left(x-y\right)\left(x+y\right)}=\dfrac{-y}{\left(x-y\right)\left(x+y\right)}\)
b: \(\dfrac{1}{x-2}+\dfrac{1}{x+2}-\dfrac{4x-4}{x^2-4}\)
\(=\dfrac{x+2+x-2-4x+4}{\left(x-2\right)\left(x+2\right)}=\dfrac{-2x+4}{\left(x-2\right)\left(x+2\right)}\)
=-2/x+2
c: \(\dfrac{x+1}{x+3}-\dfrac{x-1}{3-x}+\dfrac{2x-2x^2}{x^2-9}\)
\(=\dfrac{\left(x+1\right)\left(x-3\right)+\left(x-1\right)\left(x+3\right)+2x-2x^2}{\left(x+3\right)\left(x-3\right)}\)
\(=\dfrac{x^2-2x-3+x^2+2x-3+2x-2x^2}{\left(x+3\right)\left(x-3\right)}\)
\(=\dfrac{2x-6}{\left(x+3\right)\left(x-3\right)}=\dfrac{2}{x+3}\)
DP
1
16 tháng 2 2018
a) \(x-2=-6\)
\(x=-6+2\)
\(x=-4\)
2) \(-5x-\left(-3\right)=13\)
\(-5x+3=13\)
\(-5x=13-3\)
\(-5x=10\)
\(x=-2\)
3) \(15-\left(x-7\right)=-21\)
\(15-x+7=-21\)
\(22-x=-21\)
\(x=22+21\)
\(x=43\)
b) \(2x-\left(-17\right)=15\)
\(2x+17=15\)
\(2x=15-17\)
\(2x=-2\)
\(x=-1\)
5) \(\left|x-3\right|-7=13\)
\(\left|x-3\right|=20\)
\(\Rightarrow\orbr{\begin{cases}x-3=20\\x-3=-20\end{cases}}\Rightarrow\orbr{\begin{cases}x=23\\x=-17\end{cases}}\)
SB
2
12 tháng 7 2023
` 1, 5 . ( -2/25 = 3/2 . (-2)/25 = -6/50 = -3/25 `
` 1 3/5 . (-3)/4 = 8/5 . (-3)/4 = -24/20 = -6/5 `
`-15/4 : 21/(-1) = -15/4 . (-1)/21 = 15/84 = 5/28 `
` ( -2 1/7 ) : ( -1 1/14 ) = (-15)/7 : (-15)/14 = -15/7 . (-14)/15 = 210/105 = 2 `
`@animephamdanhv.`
8 tháng 7 2020
Bài 1 : Tính bằng cách thuận tiện
A = 3/13 x 5/7 + 2/13 x 3/7
= 2/13 + 1/13 x 5/7 + 2/13 x 3/7
= 2/13 x 72/91 + 2/13 x 3/7
= 2/13 x ( 72/91 + 3/7 )
= 2/13 x 37/24
= 37/156.
B = 21/22 x 17/8 + 21/8 x 7/22
= 21/22 x 17/8 + 17/8 + 4/8 x 7/22
= 21/22 x 17/8 + 17/8 x 7/44
= ( 21/22 + 7/44 ) x 21/22
= 31/44 x 21/22
= 651/968.
Chúc bạn học tốt!!!
26 tháng 6 2022
\(\Leftrightarrow\left(\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}+...+\dfrac{1}{19}-\dfrac{1}{21}\right)-x+\dfrac{221}{231}=\dfrac{4}{3}\)
\(\Leftrightarrow\dfrac{10}{231}+\dfrac{221}{231}-x=\dfrac{4}{3}\)
=>1-x=4/3
hay x=-1/3
x= \(\dfrac{2}{3}-\dfrac{13}{21}\)
x=\(\dfrac{1}{21}\)
x=1/21