Đáp án : `8/{27}`

Giải thích các bước giải:

`4/{3.7} + 4/{7.11} + 4/{11.15} + 4/{15.19} + 4/{19.23} + 4/{23.27}`

`= 1/3 - 1/7 + 1/7 - 1/{11} + 1/{11} - 1/{15} + 1/{15} - 1/{19} + 1/{19} - 1/{23} + 1/{23} - 1/{27}`

`= 1/3 - 1/{27}`

`= 8/{27}`

Đáp án:

Giải thích các bước giải:

$\dfrac{1}{3.7}+\dfrac{1}{7.11}+\dfrac{1}{11.15}+\dfrac{1}{15.19}+\dfrac{1}{19.23}+\dfrac{1}{23.27}$

$=\dfrac{1}{3}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{23}+\dfrac{1}{23}-\dfrac{1}{27}$

$=\dfrac{1}{3}-\left (\dfrac{1}{7}-\dfrac{1}{7}+\dfrac{1}{11}-\dfrac{1}{11}+\dfrac{1}{15}-\dfrac{1}{15}+\dfrac{1}{19}-\dfrac{1}{19}+\dfrac{1}{23}-\dfrac{1}{23} \right )-\dfrac{1}{27}$

$=\dfrac{1}{3}-\dfrac{1}{27}$

$=\dfrac{9}{27}-\dfrac{1}{27}$

$=\dfrac{8}{27}$

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