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14 tháng 4 2019
Mình lỡ đánh nhầm 2 lần \(\frac{5}{14}\)nha :)) chỉ 1 lần thôi
TG
2 tháng 5 2019
\(x\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\right)=\frac{4034}{5}\)
\(x.\frac{2}{5}=\frac{4034}{5}\)
\(x=\frac{4034}{5}:\frac{2}{5}\)
\(x=\frac{4034}{5}.\frac{5}{2}\)
x = 2017
19 tháng 2 2017
a) \(\frac{-x}{4}=\frac{-9}{x}\)
\(\Rightarrow x^2\left(-1\right)=-36\)
\(\Rightarrow x^2=6^2\)
\(\Rightarrow x=\pm6\)
Vậy \(x=\left[\begin{matrix}6\\-6\end{matrix}\right.\)
b) \(\frac{12}{x+1}=\frac{5}{30}\)
\(\Rightarrow\left(x+1\right)5=12.30\)
\(\Rightarrow5x+5=360\)
\(\Rightarrow5x=355\)
\(\Rightarrow x=355:5\)
\(\Rightarrow x=71\)
Vậy \(x=71.\)
c) \(\frac{x+42}{5}=\frac{5x+2}{20}\)
\(\Rightarrow\left(x+42\right)20=5\left(5x+2\right)\)
\(\Rightarrow20x+840=25x+10\)
\(\Rightarrow20x-25x=-840+10\)
\(\Rightarrow-5x=-830\)
\(\Rightarrow x=166\)
Vậy \(x=166.\)
19 tháng 2 2017
a, \(\frac{-x}{4}=\frac{-9}{x}\Rightarrow-x.x=-9.4\)
\(\Rightarrow-x.x=-36=-6.6\Rightarrow x=6\)
Vậy x = 6
b, \(\frac{12}{x+1}=\frac{5}{30}=\frac{1}{6}\Rightarrow x+1=12.6\)
\(\Rightarrow x+1=72\Rightarrow x=72-1=71\)
Vậy x = 71
c, \(\frac{x+42}{5}=\frac{5x+2}{20}\Rightarrow20\left(x+42\right)=5\left(5x+2\right)\)
\(\Rightarrow20x+840=25x+10\Rightarrow20x-25x=-840+10\)
\(\Rightarrow\left(20-25\right)x=-830\Rightarrow-5x=-830\)
\(\Rightarrow x=-830\div\left(-5\right)\Rightarrow x=166\)
Vậy x = 166
28 tháng 5 2018
\(\Leftrightarrow\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\times\frac{x}{3}=\frac{5}{21}\)
\(\Leftrightarrow\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\times\frac{x}{3}=\frac{5}{21}\)
\(\Leftrightarrow\left(\frac{1}{2}-\frac{1}{7}\right)\times\frac{x}{3}=\frac{5}{21}\)
\(\Leftrightarrow\frac{5}{14}\times\frac{x}{3}=\frac{5}{21}\)
\(\Leftrightarrow\frac{x}{3}=\frac{2}{3}\)
\(\Leftrightarrow x=2\)
T
28 tháng 5 2018
\(\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right).\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right).\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{6}-\frac{1}{7}\right).\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\left(\frac{1}{2}-\frac{1}{7}\right).\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\left(\frac{7}{14}-\frac{2}{14}\right).\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\frac{5}{14}.\frac{x}{3}=\frac{5}{21}\)
\(\Rightarrow\frac{x}{3}=\frac{5}{21}:\frac{5}{14}\)
\(\Rightarrow\frac{x}{3}=\frac{2}{3}\)
\(\Rightarrow x=2\)
Vậy \(x=2\)
10 tháng 7 2020
Ta có: \(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+\frac{x-2}{42}=42^5:\left(2^3\cdot21^6\right)\)
\(\Leftrightarrow\left(x-2\right)\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)=\frac{2^5\cdot21^5}{2^3\cdot21^5\cdot21}\)
\(\Leftrightarrow\left(x-2\right)\cdot\frac{4}{21}=\frac{4}{21}\)
\(\Leftrightarrow x-2=1\)
hay x=3
Vậy: x=3
T
10 tháng 9 2018
a)\(5\le2.x< 13\)''
\(\frac{5}{2}\le x< \frac{13}{2}\)( chia cho 2)
b)\(5< 4.x+1\le17\)
\(5-1< 4x\le17-1\)( trừ cho 1 )
\(4< 4x\le16\)
\(\frac{4}{4}< x\le\frac{16}{4}\)
\(1< x\le4\)
c) \(x+\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}=\frac{1}{8}\)
\(x+\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}=8\)
\(x+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}=8\)( Áp dụng \(\frac{1}{a.\left(a+1\right)}=\frac{1}{a}-\frac{1}{a+1}\))
\(x+1-\frac{1}{6}=8\)
\(x=8-1+\frac{1}{6}\)
\(x=\frac{43}{6}\)
KL
3 tháng 8 2017
a, (\(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}\)).10 - x = 0
<=> \(\dfrac{5}{6}.10-x=0\)
<=> \(\dfrac{25}{3}-x=0\)
<=> x = \(\dfrac{25}{3}\) (thỏa mãn)
@Hoàng Mạnh Quân
13 tháng 10 2017
a) A = {x E Ư(12); x < 6}
A = { 1;2;3;4}
b) B = { 24;36;48}
c) C = {15;30}
d) D = {15;20;25;30;25;40;45;50;55;.......;90;95}
P
21 tháng 6 2020
\(\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}\right).x=\frac{14}{30}\)
\(\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}\right).x=\frac{14}{30}\)
\(\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\right).x=\frac{14}{30}\)
\(\left(\frac{1}{3}-\frac{1}{10}\right).x=\frac{14}{30}\)
\(\frac{10-3}{30}.x=\frac{14}{30}\)
\(\frac{7}{30}.x=\frac{14}{30}\)
\(x=\frac{14}{30}:\frac{7}{30}\)
\(x=\frac{14}{30}.\frac{30}{7}\)
\(x=2\)
`5(12 - x) - 20 =30`
`=> 5(12 - x) = 30 + 20`
`=> 5(12 - x) = 50`
`=> 12 - x = 50 :5`
`=> 12 - x = 10`
`=> x =12 -10`
`=> x = 2`
Vậy `x=2`
dễ ....
5.(12-x)-20=30
5.(12-x) =30+20
5.(12-x) =50
12-x =50:5
12-x =10
x =12-10
x =2
Vậy x = 2