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Darkness Evolution

Duke of Mathematics
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27 Tháng năm 2020
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Vĩnh Phúc
THCS Vĩnh Yên
[tex]P=\left ( 1+\frac{1}{6} \right )+\left ( 1+\frac{1}{12} \right )+\left ( 1+\frac{1}{20} \right )+ ... +\left ( 1+\frac{1}{90} \right )[/tex]
[tex]P=(1+1+1+...+1)+\left ( \frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90} \right )[/tex]
[tex]P=8+\left ( \frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\frac{1}{4\cdot 5}+...+\frac{1}{9\cdot 10} \right )[/tex]
[tex]P=8+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}[/tex]
[tex]P=8+\frac{1}{2}-\frac{1}{10}=\frac{42}{5}[/tex]
 
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