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![](https://rs.olm.vn/images/avt/0.png?1311)
\(S=1-2+3-4+...+199-200+201\)
\(=\left(1-2\right)+\left(3-4\right)+...+\left(199-200\right)+201\)
\(=1+1+...+1+201\)
\(=\dfrac{200}{2}+201\)
\(=301\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Answer:
\(\left(x-\dfrac{1}{2}\right)^2=4\)
\(\left(x-\dfrac{1}{2}\right)^2=\left(\pm2\right)^2\)
TH1: \(\left(x-\dfrac{1}{2}\right)^2=2^2\)
\(x-\dfrac{1}{2}=2\)
\(x=2+\dfrac{1}{2}\)
\(x=\dfrac{5}{2}\)
TH2: \(\left(x-\dfrac{1}{2}\right)^2=\left(-2\right)^2\)
\(x-\dfrac{1}{2}=-2\)
\(x=-2+\dfrac{1}{2}\)
\(x=\dfrac{-3}{2}\)
\(\Rightarrow\left\{{}\begin{matrix}x=\dfrac{5}{4}\\x=\dfrac{-3}{2}\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Giải:
(1-1/22).(1-1/32).(1-1/42).....(1-1/102)
=3/2.2 . 8/3.3 . 15/4.4 . ... . 99/10.10
=1.3.2.4.3.5.....9.11/2.2.3.3.4.4.....10.10
=1.2.3.....9/2.3.4.....10 . 3.4.5....11/2.3.4.....10
=1/10.11/2
=11/20
Chúc bạn học tốt!
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