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5 tháng 7 2017

\(\dfrac{5}{6}-\dfrac{1}{2}\left(x-\dfrac{1}{3}\right)-\dfrac{2}{5}x=0\Rightarrow\dfrac{1}{2}\left(x-\dfrac{1}{3}\right)-\dfrac{2}{5}x=\dfrac{5}{6}\)

\(\Rightarrow\dfrac{1}{2}x-\dfrac{1}{6}-\dfrac{2}{5}x=\dfrac{5}{6}\Rightarrow\dfrac{1}{2}x-\dfrac{2}{5}x=\dfrac{5}{6}+\dfrac{1}{6}=1\)

\(\Rightarrow x\left(\dfrac{1}{2}-\dfrac{2}{5}\right)=1\Rightarrow\dfrac{1}{10}x=1\Rightarrow x=1:\dfrac{1}{10}=10\)

Vậy x = 10

15 tháng 9 2017

1)|x|+|1-x|+|x+2|=5

<=>x+1-x+x+2=5

<=>x=5-2-1

<=>x=2

16 tháng 9 2017

cau 2 cau hoi la |x-1/2|+|y+2/3|+|x^2+xz| nha, ko phai la 2\3 ma la 2/3

18 tháng 6 2016

a) \(\Leftrightarrow\left|2x-3\right|=\frac{1}{4}\Leftrightarrow\orbr{\begin{cases}x\ge\frac{3}{2}\mid:2x-3=\frac{1}{4}\Rightarrow2x=\frac{13}{4}\Rightarrow x=\frac{13}{8}\left(TM\right)\\x< \frac{3}{2}\mid:3-2x=\frac{1}{4}\Rightarrow2x=\frac{11}{4}\Rightarrow x=\frac{11}{8}\left(TM\right)\end{cases}.}\)

b) \(\Leftrightarrow\left|x-1\right|=\frac{3}{4}\Leftrightarrow\orbr{\begin{cases}x\ge1\mid:x-1=\frac{3}{4}\Rightarrow x=\frac{7}{4}\left(TM\right)\\x< 1\mid:1-x=\frac{3}{4}=>x=\frac{1}{4}\left(TM\right)\end{cases}}\)

c) \(\frac{3}{5\left(x-\frac{5}{6}\right)}-\frac{1}{2\left(\frac{3}{2}-1\right)}=-\frac{1}{4}\Leftrightarrow\frac{3}{\frac{5\left(6x-5\right)}{6}}-\frac{1}{2\cdot\frac{1}{2}}=-\frac{1}{4}\Leftrightarrow\frac{18}{5\left(6x-5\right)}=-\frac{1}{4}+1\)

\(\Leftrightarrow\frac{18}{5\left(6x-5\right)}=\frac{3}{4}\Leftrightarrow6x-5=\frac{24}{5}\Leftrightarrow6x=\frac{49}{5}\Leftrightarrow x=\frac{49}{30}\)

d) \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2016}\)

\(\Leftrightarrow\frac{2}{2\cdot3}+\frac{2}{3\cdot4}+\frac{2}{4\cdot5}+...+\frac{2}{x\left(x+1\right)}=\frac{2015}{2016}\)

\(\Leftrightarrow2\cdot\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2015}{2016}\)

\(\Leftrightarrow2\left(\frac{1}{2}-\frac{1}{x+1}\right)=\frac{2015}{2016}\Leftrightarrow2\cdot\frac{x+1-2}{2\left(x+1\right)}=\frac{2015}{2016}\Leftrightarrow\frac{x-1}{x+1}=\frac{2015}{2016}\)

\(\Leftrightarrow2016x-2016=2015x+2015\Leftrightarrow x=2015+2016=4031\)

Vậy x = 4031.

5 tháng 8 2017

(x+1/5) -4 = -2

x= -6-1/5

x= -31/5

5 tháng 8 2017

Ta có : \(\left(2x+3\right)\left(x-7\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}2x+3=0\\x-7=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}2x=-3\\x=7\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=-\frac{3}{2}\\x=7\end{cases}}\)