2x +2x+1+2x+2=960-2x+3
tìm x
K
Khách
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H
14 tháng 4 2023
\(2^x+2^{x+1}+2^{x+2}=960-2^{x+3}\\ \Leftrightarrow2^x+2^{x+1}+2^{x+2}+2^{x+3}=960\\ \Leftrightarrow2^x+2^x.2+2^x.2^2+2^x.2^3=960\\ \Leftrightarrow2^x\left(1+2+2^2+2^3\right)=960\\ \Leftrightarrow2^x.15=960\\ \Leftrightarrow2^x=64\\ \Leftrightarrow2^x=2^6\\ \Leftrightarrow x=6\)
Vậy \(x=6\)
3 tháng 7 2021
\(\)đặt \(2x^2+y^2+\dfrac{28}{x}+\dfrac{1}{y}=A\)
\(=>A=2x^2+y^2-7x-y+\dfrac{28}{x}+7x+\dfrac{1}{y}+y\)
\(A=2x^2-8x+8+y^2-2y+1+x+y-9+\dfrac{28}{x}+7x+\dfrac{1}{y}+y\)
\(A=2\left(x-2\right)^2+\left(y-1\right)^2+\left(x+y\right)-9+\dfrac{28}{x}+7x+\dfrac{1}{y}+y\)
áp dụng BDT AM-GM\(=>\dfrac{28}{x}+7x+\dfrac{1}{y}+y\ge2\sqrt{28.7}+2\sqrt{1}=30\)
\(=>A\ge30+3-9=24\)
dấu"=" xảy ra<=>x=2,y=1
31 tháng 10 2021
\(\Leftrightarrow\left(x^2+2x\right)^2-2\left(x^2+2x\right)-3=0\)
\(\Leftrightarrow\left(x^2+2x-3\right)\left(x^2+2x+1\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x-1\right)\left(x+1\right)^2=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=1\\x=-1\end{matrix}\right.\)
TH
1
TH
1
HN
2 tháng 4 2022
f(x)=0 \(\Leftrightarrow\) 2x+a2-3=0 \(\Rightarrow\) x=\(\dfrac{3-a^2}{2}\).
a) x=1 \(\Leftrightarrow\) \(\dfrac{3-a^2}{2}\)=1 \(\Rightarrow\) a=\(\pm\)1.
b) x=\(\dfrac{-1}{2}\) \(\Leftrightarrow\) \(\dfrac{3-a^2}{2}\)=\(\dfrac{-1}{2}\) \(\Rightarrow\) a=\(\pm\)2.
VD
20 tháng 3 2022
a,ĐKXĐ:\(\left\{{}\begin{matrix}x\ne\pm1\\x\ne\dfrac{1}{2}\end{matrix}\right.\)
\(A=\left(\dfrac{2}{x+1}-\dfrac{1}{x-1}+\dfrac{5}{x^2-1}\right):\dfrac{2x+1}{x^2-1}\\ =\left(\dfrac{2\left(x-1\right)}{\left(x+1\right)\left(x-1\right)}-\dfrac{x+1}{\left(x+1\right)\left(x-1\right)}+\dfrac{5}{\left(x+1\right)\left(x-1\right)}\right).\dfrac{\left(x-1\right)\left(x+1\right)}{2x+1}\\ =\dfrac{2x-2-x-1+5}{\left(x+1\right)\left(x-1\right)}.\dfrac{\left(x-1\right)\left(x+1\right)}{2x+1}\\ =\dfrac{x+2}{2x+1}\)
\(b,A=3\\ \Leftrightarrow\dfrac{x+2}{2x+1}=3\\ \Leftrightarrow6x+3=x+2\\ \Leftrightarrow5x+1=0\\ \Leftrightarrow x=-\dfrac{1}{5}\left(tm\right)\)
\(c,\dfrac{1}{A}=\dfrac{2x+1}{x+2}=\dfrac{2x+4-3}{x+2}=\dfrac{2\left(x+2\right)-3}{x+2}=2-\dfrac{3}{x+2}\)
Để `1/A` là số nguyên thì `3/(x+2)` nguyên \(\Rightarrow x+2\inƯ\left(3\right)=\left\{-3;-1;1;3\right\}\)
Ta có bảng:
| x+2 | -3 | -1 | 1 | 3 |
| x | -5 | -3 | -1(ktm) | 1(ktm) |
Vậy \(x\in\left\{-5;-3\right\}\)
C
1
NV
Nguyễn Việt Lâm
Giáo viên
20 tháng 7 2021
Ta có:
\(3-S=\left(x^2+4y^2+9z^2\right)-\left(2x+4y+6z\right)\)
\(\Rightarrow3-S=\left(x^2-2x+1\right)+\left(4y^2-4y+1\right)+\left(9z^2-6z+1\right)-3\)
\(\Rightarrow6-S=\left(x-1\right)^2+\left(2y-1\right)^2+\left(3z-1\right)^2\ge0\)
\(\Rightarrow S\le6\)
\(S_{max}=6\) khi \(\left\{{}\begin{matrix}x-1=0\\2y-1=0\\3z-1=0\end{matrix}\right.\) \(\Leftrightarrow\left(x;y;z\right)=\left(1;\dfrac{1}{2};\dfrac{1}{3}\right)\)
\(2^x+2^{x+1}+2^{x+2}=960-2^{x+3}\)
\(\Leftrightarrow2^x+2^{x+1}+2^{x+2}+2^{x+3}=960\)
\(\Leftrightarrow2^x\left(1+2+2^2+2^3\right)=960\)
\(\Leftrightarrow2^x.15=960\)
\(\Leftrightarrow2^x=64\)
\(\Leftrightarrow2^x=2^6\Leftrightarrow x=6\)
Vậy...