[Toán 6] Chứng tỏ

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$1+\dfrac{1}{2}+\dfrac{1}{3}+....+\dfrac{1}{50}=1+\dfrac{1}{2}+\dfrac{1}{3}+....+\dfrac{1}{50}$

$\rightarrow \dfrac{1}{26}+\dfrac{1}{27}+...+\dfrac{1}{50}+2( \dfrac { 1 } { 2 } +\dfrac{1}{4}+...+\dfrac{1}{50})=1+ \dfrac { 1 } { 2 } +\dfrac{1}{3}+....+\dfrac{1}{50}$

$\rightarrow \dfrac{1}{26}+\dfrac{1}{27}+...+\dfrac{1}{50}=1-\dfrac{1}{2}+\dfrac{1}{3}-...-\dfrac{1}{50}(dpcm)$
 
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