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\(\frac{1}{x\left(x+1\right)}=\frac{\left(x+1\right)-x}{x\left(x+1\right)}=\frac{x+1}{x\left(x+1\right)}-\frac{x}{x\left(x+1\right)}=\frac{1}{x}-\frac{1}{x+1}\)
=>\(\frac{1}{x}-\frac{1}{x+1}=\frac{1}{x}+\frac{1}{2011}\)
=>\(\frac{1}{x}-\frac{1}{x+1}-\frac{1}{x}=\frac{1}{2011}\)
=>\(\frac{1}{x}-\frac{1}{x}-\frac{1}{x+1}=\frac{1}{2011}\)
=>\(0-\frac{1}{x+1}=\frac{1}{2011}\)
=>\(-\frac{1}{x+1}=\frac{1}{2011}\)
=>-x+1=2011
=>-x=2011-1
=>-x=2010
=>x=-2010
Vậy x=-2010
\(\frac{1}{x\left(x+1\right)}=\frac{1}{x}+\frac{1}{2011}\)
<=>\(\frac{1}{x}-\frac{1}{x+1}=\frac{1}{x}+\frac{1}{2011}\)
<=>\(-\frac{1}{x+1}=\frac{1}{2011}\)
<=>-x-1=2011
<=>x=-2012
Đáp số: \(x=-2012\)
\(\frac{|x|}{186}=\left(1-\frac{30}{31}\right)+\left(\frac{60}{61}-1\right)\)
\(\Leftrightarrow|x|=186\left(\frac{1}{31}-\frac{1}{61}\right)\)
\(\Leftrightarrow|x|=6-\frac{186}{61}\)
\(\Leftrightarrow|x|=\frac{180}{61}\)
\(\Leftrightarrow x=\pm\frac{180}{61}\)
Giá trị của x thỏa mãn:
\(\left(\frac{1}{2}\right)^{x+4}=\left(\frac{1}{4}\right)^{\frac{3}{2}.x-4}\)
\(\left(\frac{1}{2}\right)^{x+4}=\left(\frac{1}{4}\right)^{\frac{3}{2}x-4}\)
=> \(\left(\frac{1}{2}\right)^{x+4}=\left(\frac{1}{2}\right)^{2\left(\frac{3}{2}x-4\right)}\)
=> \(\left(\frac{1}{2}\right)^{x+4}=\left(\frac{1}{2}\right)^{3x-8}\)
=> \(x+4=3x-8\)
=> \(3x-8-x=4\)
=> \(2x-8=4\)
=> \(2x=12\)
=> \(x=\frac{12}{2}=6\)
\(\left(\frac{1}{2}\right)^{-x+4}=\left(\frac{1}{4}\right)^{\frac{3}{2}x-4}\)
=>\(\left(\frac{1}{2}\right)^{-x+4}=\left(\frac{1}{2}\right)^{3x-8}\)
=>-x+4=3x-8
<=>4x=12
<=>x=3
Vậy x=3
\(\left(\frac{1}{4}\right)^{\frac{3}{2}-4}=\left(\frac{1}{2}\right)^{2.\left(\frac{3}{2}-4\right)}=\left(\frac{1}{2}\right)^{-1}\)
; do đó -x + 4 = -1
=> -x = -1 - 4 = -5
=> x = 5
4. (3/4-81)(3^2/5-81)(3^3/6-81)....(3^6/9-81).....(3^2011/2014-81)
mà 3^6/9-81=0 => (3/4-81)(3^2/5-81)....(3^2011/2014-81)=0
Câu 1:
Ta thấy:
\(\left(x-\frac{2}{5}\right)^2\ge0\Rightarrow\frac{1}{3}\cdot\left(x-\frac{2}{5}\right)^2\ge0\)
\(\left|2y+1\right|\ge0\)
\(\Rightarrow\frac{1}{3}\cdot\left(x-\frac{2}{5}\right)^2+\left|2y+1\right|\ge0\)
\(\Rightarrow\frac{1}{3}\cdot\left(x-\frac{2}{5}\right)^2+\left|2y+1\right|-2,5\ge-2,5\)
hay \(A\ge-2,5\)
Dấu "=" xảy ra khi \(\begin{cases}\left(x-\frac{2}{5}\right)^2=0\\\left|2y+1\right|=0\end{cases}\)
\(\Rightarrow\begin{cases}x-\frac{2}{5}=0\\2y+1=0\end{cases}\)
\(\Rightarrow\begin{cases}x=\frac{2}{5}\\2y=-1\end{cases}\)
\(\Rightarrow\begin{cases}x=\frac{2}{5}\\y=-\frac{1}{2}\end{cases}\)
Vậy GTNN của A là -2,5 đạt được khi \(\begin{cases}x=\frac{2}{5}\\y=-\frac{1}{2}\end{cases}\)
