tìm x , biết
\(a,(x-\frac{1}{2})\times2=\frac{9}{16}\)
\(b,|x+\frac{1}{2}|=\frac{3}{4}\)
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YY
24 tháng 4 2018
\(\frac{2}{5}x+\frac{3}{10}=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.........+\frac{1}{9}-\frac{1}{10}\)
\(\frac{2}{5}x+\frac{3}{10}=1-\frac{1}{10}=\frac{9}{10}\)
\(\frac{2}{5}x=\frac{9}{10}-\frac{3}{10}=\frac{3}{5}\)
\(x=\frac{\frac{3}{5}}{\frac{2}{5}}=\frac{3}{2}\)
PY
24 tháng 4 2018
Ta có: \(\frac{1}{1x2}\)+ \(\frac{1}{2x3}\)+ \(\frac{1}{3x4}\)+ \(\frac{1}{4x5}\)+ .....+ \(\frac{1}{9x10}\)
= \(1-\left(\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-.....-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\right)\)
= 1 - \(\frac{1}{10}\)
= \(\frac{9}{10}\)
TL
1
IA
9 tháng 6 2018
\(\Leftrightarrow10\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{x\times\left(x+1\right)}\right)=9\)
\(\Leftrightarrow\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}\right)=9\div10\)
\(\Leftrightarrow\frac{1}{1}-\frac{1}{x+1}=\frac{9}{10}\)
\(\Leftrightarrow\frac{1}{x+1}=1-\frac{9}{10}\)
\(\Leftrightarrow\frac{1}{x+1}=\frac{1}{10}\)
\(\Rightarrow x+1=10\)
\(\Leftrightarrow x=9\)
Vậy x = 9
2 tháng 6 2015
( 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 +1/5.6 ) x 10 - x = 0
= ( 1- 1/2 +1/2 -1/3 +1/3 - 1/4 + 1/4 - 1/5 +1/5 -1/6 ) x 10 - x = 0
= ( 1 - 1/6 ) x 10 - x = 0
= 5/6 x 10 - x =0
= 25/3 - x =0
x = 25/3 - 0
x = 25/3
MT
2 tháng 6 2015
\(\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}\right)\times10-x=0\)
\(\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\right)\times10-x=0\)
\(\left(\frac{1}{1}-\frac{1}{6}\right)\times10-x=0\)
\(\frac{5}{6}\times10-x=0\)
\(\frac{25}{3}-x=0\)
x =\(\frac{25}{3}-0=\frac{25}{3}\)
16 tháng 8 2015
Ta co:
\(\left[\left(\frac{29}{25}-x\right).\frac{21}{4}\right]:\left[\left(\frac{95}{9}-\frac{29}{4}\right).\frac{36}{17}\right]=\frac{3}{4}\)
\(\left[\left(\frac{29}{25}-x\right).\frac{21}{4}\right]:\left(\frac{119}{36}.\frac{36}{17}\right)=\frac{3}{4}\)
\(\left[\left(\frac{29}{25}-x\right).\frac{21}{4}\right]:7=\frac{3}{4}\)
\(\left(\frac{29}{25}-x\right).\frac{21}{4}=\frac{3}{4}.7=\frac{21}{4}\)
\(\frac{29}{25}-x=\frac{21}{4}:\frac{21}{4}=1\)
\(x=\frac{29}{25}-1=\frac{4}{25}\)
2 tháng 4 2018
\(a)\) \(-\left(x+84\right)+213=-16\)
\(\Leftrightarrow\)\(-x-84+213=-16\)
\(\Leftrightarrow\)\(x=213-84+16\)
\(\Leftrightarrow\)\(x=145\)
Vậy \(x=145\)
\(b)\) \(\left(x-1\right)^2=\left|\frac{1}{4}-\frac{1}{2}-\frac{3}{4}\right|\)
\(\Leftrightarrow\)\(\left(x-1\right)^2=\left|-1\right|\)
\(\Leftrightarrow\)\(\left(x-1\right)^2=1\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}x-1=1\\x-1=-1\end{cases}\Leftrightarrow\orbr{\begin{cases}x=2\\x=0\end{cases}}}\)
Vậy \(x=0\) hoặc \(x=2\)
Chúc bạn học tốt ~
NT
2 tháng 4 2018
a) \(-\left(x+84\right)+213=-16\)
\(-\left(x+84\right)=-16-213\)
\(-\left(x+84\right)=-229\)
\(\Rightarrow x+84=229\)
\(\Rightarrow x=229-84=145\)
Vậy \(x=145\)
b) \(\left(x-1\right)^2=\left|\frac{1}{4}-\frac{1}{2}-\frac{3}{4}\right|\)
\(\left(x-1\right)^2=\left|\frac{-1}{4}-\frac{3}{4}\right|\)
\(\left(x-1\right)^2=\left|-1\right|\)
\(\left(x-1\right)^2=1\)
\(\Rightarrow\orbr{\begin{cases}x-1=1\\x-1=-1\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x=1+1=2\\x=-1+1=0\end{cases}}\)
Vậy \(x\in\left\{0;2\right\}\)
RR
0
2 tháng 8 2016
a) \(\frac{\left(3.4.2^{16}\right)^2}{11.2^{13}.4^{11}-16^9}=\frac{\left(3.2^2.2^{16}\right)^2}{11.2^{13}.\left(2^2\right)^{11}-\left(2^4\right)^9}\)
\(=\frac{\left(3.2^{18}\right)^2}{11.2^{13}.2^{22}-2^{36}}\)
\(=\frac{3^2.2^{36}}{11.2^{35}-2^{36}}\)
\(=\frac{9.2^{36}}{2^{35}.\left(11-2\right)}\)
\(=\frac{9.2^{36}}{2^{35}.9}=2\)
b) \(\frac{3}{2}.x-\left(\frac{4}{5}-2.x\right)=1\frac{3}{10}:\frac{3}{2}\)
\(\frac{3}{2}.x-\frac{4}{5}+2.x=\frac{13}{10}:\frac{3}{2}\)
\(\left(\frac{3}{2}.x+2.x\right)-\frac{4}{5}=\frac{13}{10}.\frac{2}{3}\)
\(x.\left(\frac{3}{2}+2\right)-\frac{4}{5}=\frac{13}{15}\)
\(x.\frac{7}{2}=\frac{13}{15}+\frac{4}{5}\)
\(x.\frac{5}{2}=\frac{13}{15}+\frac{12}{15}\)
\(x.\frac{7}{2}=\frac{25}{15}=\frac{5}{3}\)
\(x=\frac{5}{3}:\frac{7}{2}\)
\(x=\frac{5}{3}.\frac{2}{7}=\frac{10}{21}\)
a) (x - 1/2) x 2 = 9/16
=> x - 1/2 = 9/16 : 2
=> x - 1/2 = 9/16 x 1/2
=> x - 1/2 =9/32
=> x = 9/32 + 1/2
=> x = 25/32
b) |x + 1/2| = 3/4
=> x + 1/2 = 3/4 hoặc x + 1/2 =-3/4
=>x = 3/4 - 1/2 hoặc x = -3/4 -1/2
=>x = 1/4 hoặc x = -5/4
Vậy .........