3.3=?
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{3.3}{20.23}+\dfrac{3.3}{23.26}+...+\dfrac{3.3}{77.80}\)
\(=3\left(\dfrac{3}{20.23}+\dfrac{3}{23.26}+...+\dfrac{3}{77.80}\right)\)
\(=3\left(\dfrac{1}{20}-\dfrac{1}{23}+\dfrac{1}{23}-\dfrac{1}{26}+...+\dfrac{1}{77}-\dfrac{1}{80}\right)\)
\(=3\left(\dfrac{1}{20}-\dfrac{1}{80}\right)\)
\(=3.\dfrac{3}{80}=\dfrac{9}{80}< 1\left(đpcm\right)\)
Vậy...
![](https://rs.olm.vn/images/avt/0.png?1311)
=> 1+2+3+4+5+....+x = 190
x(x+1) = 190.2 = 380
x(x+1) = 19.(19 + 1)
VẬy x = 19
![](https://rs.olm.vn/images/avt/0.png?1311)
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
![](https://rs.olm.vn/images/avt/0.png?1311)
\(3\cdot3^2\cdot3^3\cdot3^4\cdot....\cdot3^x=3^{190}\)
\(\Leftrightarrow3^{1+2+3+...+x}=3^{190}\)
\(\Leftrightarrow1+2+3+...+x=190\)
\(\Leftrightarrow\dfrac{x\left(x+1\right)}{2}=190\Leftrightarrow x\left(x+1\right)=380\)
\(\Leftrightarrow x^2+x-380=0\)
\(\Leftrightarrow x^2-19x+20x-380=0\)
\(\Leftrightarrow x\left(x-19\right)+20\left(x-19\right)=0\)
\(\Leftrightarrow\left(x-19\right)\left(x+20\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-19=0\\x+20=0\end{matrix}\right.\)\(\Leftrightarrow x=19\left(x>0\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
![](https://rs.olm.vn/images/avt/0.png?1311)
3.3=9
ai k mình
mình k lại
3.3=9
chúc bạn may mắn!