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3.32.33.34......3x=3190
=>3(1+2+3+...........+x)=3190
=>1+2+3+.........+x=190
=>\(\frac{x.\left(x+1\right)}{2}\)=180
=>x.(x+1)=190.2
=>x.(x+1)=380
=>x=19
=> 1+2+3+4+5+....+x = 190
x(x+1) = 190.2 = 380
x(x+1) = 19.(19 + 1)
VẬy x = 19
=>31+2+3+4+...+x=3190
=>1+2+3+4+...+x=190
=>(x+1).x:2=190
=>(x+1).x=380
mà 380 chỉ có thể ptích thành: 380=20.19
=>x+1=20 và x=19
vậy x=19
3.3^2.3^3.............3^x=3^190
3^1+2+3+4+....+x=3^190
nên 1+2+3+.........+x=190
hay (x+1).x :2 =190 nen 190.2= (x+1) . x hay 380 =19.20
vay x=19
ta có
\(3^{1+2+3+..+x}=3^{3.12}\Leftrightarrow\frac{x\left(x+1\right)}{2}=36\)
\(\Leftrightarrow x.\left(x+1\right)=72=8.9\Leftrightarrow x=8\)
b. ta có
\(5A=1+\frac{1}{5}+\frac{1}{5^2}+..+\frac{1}{5^{2016}}=\left(\frac{1}{5}+\frac{1}{5^2}+..+\frac{1}{5^{2016}}+\frac{1}{5^{2017}}\right)+1-\frac{1}{5^{2017}}\)
\(=A+1-\frac{1}{5^{2017}}\Rightarrow4A=1-\frac{1}{5^{2017}}< 1\Rightarrow A< \frac{1}{4}\)
a/ \(|5x-3|< 2\) b/ \(|3x+1>4|\) c/ \(|4-x|+2x=3\)
\(\Leftrightarrow5x-3< 2\) \(\Leftrightarrow3x+1>4\) \(\Leftrightarrow4-x+2x=3\)
\(\Leftrightarrow5x< 5\) \(\Leftrightarrow3x>3\) \(\Leftrightarrow x=-1\)
\(\Leftrightarrow x< 1\) \(\Leftrightarrow x>1\)
\(a,\left|5x-3\right|< 2\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}\left|5x-3\right|=1\\\left|5x-3\right|=0\end{cases}}\)
\(TH1:\)\(\)
\(\left|5x-3\right|=1\)
\(\Leftrightarrow\orbr{\begin{cases}5x-3=1\\5x-3=-1\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}5x=1+3\\5x=-1+3\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}5x=4\\5x=2\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=\frac{4}{5}\left(\text{loại}\right)\\x=\frac{2}{5}\left(\text{loại}\right)\end{cases}}\)
\(TH2:\)
\(\left|5x-3\right|=0\)
\(\Leftrightarrow5x-3=0\)
\(\Leftrightarrow5x=0+3\)
\(\Leftrightarrow5x=3\)
\(\Leftrightarrow x=\frac{3}{5}\left(\text{loại}\right)\)
\(\text{Vậy : không tồn tại x cần tìm.}\)
\(b,\left|3x+1\right|>4\)
\(\Leftrightarrow\orbr{\begin{cases}3x+1>4\\3x+1< -4\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}3x>4-1\\3x< -4-1\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}3x>3\\3x< -5\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x>3\div3\\x< -5\div3\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x>1\\x< \frac{-5}{3}\end{cases}}\)
\(\text{Vậy : }\)\(x>1\)\(\text{hoặc}\)\(x< \frac{-5}{3}\)
\(\)
\(3\cdot3^2\cdot3^3\cdot3^4\cdot....\cdot3^x=3^{190}\)
\(\Leftrightarrow3^{1+2+3+...+x}=3^{190}\)
\(\Leftrightarrow1+2+3+...+x=190\)
\(\Leftrightarrow\dfrac{x\left(x+1\right)}{2}=190\Leftrightarrow x\left(x+1\right)=380\)
\(\Leftrightarrow x^2+x-380=0\)
\(\Leftrightarrow x^2-19x+20x-380=0\)
\(\Leftrightarrow x\left(x-19\right)+20\left(x-19\right)=0\)
\(\Leftrightarrow\left(x-19\right)\left(x+20\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-19=0\\x+20=0\end{matrix}\right.\)\(\Leftrightarrow x=19\left(x>0\right)\)
dễ thì làm đi =="