1 . Tìm \(x\) sao cho : 3 - ( 2 . \(x\)+ \(\frac{1}{2}\)) : \(\frac{1}{2}\)= 2
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QT
2
5 tháng 4 2018
\(\left(\frac{1}{x}-\frac{2}{3}\right)^2-\frac{1}{16}=0\)
\(\left(\frac{1}{x}-\frac{2}{3}\right)^2=\frac{1}{16}\)
Ta có 2 trường hợp :
TH1 : \(\frac{1}{x}-\frac{2}{3}=\frac{1}{4}\)
\(\Leftrightarrow\frac{1}{x}=\frac{11}{12}\)
\(\Leftrightarrow x=\frac{12}{11}\)
TH2 : \(\frac{1}{x}-\frac{2}{3}=-\frac{1}{4}\)
\(\Leftrightarrow\frac{1}{x}=\frac{5}{12}\)
\(\Leftrightarrow x=\frac{12}{5}\)
BT
5 tháng 4 2018
\(\left(\frac{1}{x}-\frac{2}{3}\right)^2-\frac{1}{16}=0\) <=> \(\left(\frac{1}{x}-\frac{2}{3}\right)^2=\left(\frac{1}{4}\right)^2\)
=> \(|\frac{1}{x}-\frac{2}{3}|=\frac{1}{4}\)=> \(\frac{1}{x}-\frac{2}{3}=\pm\frac{1}{4}\)
+/ TH1: \(\frac{1}{x}=\frac{2}{3}+\frac{1}{4}=\frac{11}{12}=>x=\frac{12}{11}\)
+/ TH2: \(\frac{1}{x}=\frac{2}{3}-\frac{1}{4}=\frac{5}{12}=>x=\frac{12}{5}\)
8 tháng 3 2020
\(x^2+y+\frac{3}{4}\ge x^2+\frac{1}{4}+y+\frac{1}{2}\ge2\sqrt{x^2\cdot\frac{1}{4}}+\left(y+\frac{1}{2}\right)\ge x+y+\frac{1}{2}\)
\(\Rightarrow VT\ge\left(x+y+\frac{1}{2}\right)^2=\left[\left(x+\frac{1}{4}\right)+\left(y+\frac{1}{4}\right)\right]^2\ge4\left(x+\frac{1}{4}\right)\left(y+\frac{1}{4}\right)\)
\(=\left(2x+\frac{1}{2}\right)\left(2y+\frac{1}{2}\right)\)
Dấu "=" xảy ra tại \(x=y=\frac{1}{2}\)
Vậy \(x=y=\frac{1}{2}\)
8 tháng 3 2020
\(PT\Leftrightarrow x^2y^2+y^3+x^3+\frac{3}{4}\left(x^2+y^2\right)+xy+\frac{3}{4}\left(x+y\right)+\frac{9}{16}=4xy+x+y+\frac{1}{4}.\)
\(\Leftrightarrow x^2y^2+\left(x+y\right)^3-3xy\left(x+y\right)+\frac{3}{4}\left[\left(x+y\right)^2-2xy\right]+\frac{1}{4}\left(x+y\right)-3xy+\frac{5}{16}=0\)
Đặt \(x+y=a,xy=b\)
\(\Rightarrow b^2+a^3-3ab+\frac{3}{4}\left(a^2-2b\right)+\frac{a}{4}-3b+\frac{5}{16}=0\)
\(\Leftrightarrow16b^2+16a^3-48ab+12a^2-24b+4a-48b+5=0\)
\(\Leftrightarrow16b^2+16a^3-48ab+12a^2-72b+4a+5=0\)
Đến đây phân tích thành nhân tử hay sao ấy, chưa nghĩ ra :P
25 tháng 11 2019
a) A = \(\frac{3x^2+3x-3}{x^2+x-2}-\frac{x+1}{x+2}+\frac{x-2}{x}\cdot\left(\frac{1}{1-x}-1\right)\)
A = \(\frac{3x^2+3x-3}{x^2+2x-x-2}-\frac{x+1}{x+2}+\frac{x-2}{x}\cdot\left(\frac{1-1+x}{1-x}\right)\)
A = \(\frac{3x^2+3x-3}{\left(x-1\right)\left(x+2\right)}-\frac{x+1}{x+2}+\frac{x-2}{x}\cdot\frac{x}{1-x}\)
A = \(\frac{3x^2+3x-3}{\left(x-1\right)\left(x+2\right)}-\frac{x+1}{x+2}-\frac{x-2}{x-1}\)
A = \(\frac{3x^2+3x-3}{\left(x-1\right)\left(x+2\right)}-\frac{\left(x+1\right)\left(x-1\right)}{\left(x-1\right)\left(x+2\right)}-\frac{\left(x-2\right)\left(x+2\right)}{\left(x-1\right)\left(x+2\right)}\)
A = \(\frac{3x^2+3x-3-x^2+1-x^2+4}{\left(x-1\right)\left(x+2\right)}\)
A = \(\frac{x^2+3x+2}{\left(x-1\right)\left(x+2\right)}\)
A = \(\frac{x^2+2x+x+2}{\left(x-1\right)\left(x+2\right)}\)
A = \(\frac{\left(x+1\right)\left(x+2\right)}{\left(x-1\right)\left(x+2\right)}\)
A = \(\frac{x+1}{x-1}\) (Đk: \(x-1\ge0\) => x \(\ge\)1)
b) Ta có: A = \(\frac{x+1}{x-1}=\frac{\left(x-1\right)+2}{x-1}=1+\frac{2}{x-1}\)
Để A \(\in\)Z <=> 2 \(⋮\)x - 1
<=> x - 1 \(\in\)Ư(2) = {1; -1; 2; -2}
<=> x \(\in\){2; 0; 3; -1}
c) Ta có: A < 0
=> \(\frac{x+1}{x-1}< 0\)
=> \(\hept{\begin{cases}x+1< 0\\x-1>0\end{cases}}\) hoặc \(\hept{\begin{cases}x+1>0\\x-1< 0\end{cases}}\)
=> \(\hept{\begin{cases}x< -1\\x>1\end{cases}}\)(loại) hoặc \(\hept{\begin{cases}x>-1\\x< 1\end{cases}}\)
=> -1 < x < 1
25 tháng 11 2019
Edogawa Conan
Thiếu dòng đầu \(ĐKXĐ:\hept{\begin{cases}x\ne1\\x\ne-2\\x\ne0\end{cases}}\)
18 tháng 2 2018
6) Ta có
\(A=\frac{x^3}{y+2z}+\frac{y^3}{z+2x}+\frac{z^3}{x+2y}\)
\(=\frac{x^4}{xy+2xz}+\frac{y^4}{yz+2xy}+\frac{z^4}{zx+2yz}\)
\(\ge\frac{\left(x^2+y^2+z^2\right)^2}{xy+2xz+yz+2xy+zx+2yz}\)
\(\Leftrightarrow A\ge\frac{1}{3\left(xy+yz+zx\right)}\ge\frac{1}{3\left(x^2+y^2+z^2\right)}=\frac{1}{3}\)
Dấu chấm là dấu nhân nhé !
\(3-\left(2x+\frac{1}{2}\right):\frac{1}{2}=2\)
= \(3-2x-\frac{1}{2}:\frac{1}{2}=2\)
= \(3-2x-1=2\)
= \(3-2x=2+1\)
= \(3-2x=3\)
\(2x=3-3\)
\(2x=0\)
\(x=0:2\)
\(x=0\)