Câu hỏi của Phạm Gia Khánh

Question

B=1/1.6+1/6.11+1/11.16+...+1/101.106

Võ Ngọc Phương · Accepted Answer

$B=\dfrac{1}{1.6}+\dfrac{1}{6.11}+\dfrac{1}{11.16}+...+\dfrac{1}{101.106}$

$B=\dfrac{1}{5}.\left(1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}+...+\dfrac{1}{101}-\dfrac{1}{106}\right)$

$B=\dfrac{1}{5}.\left(1-\dfrac{1}{106}\right)$

$B=\dfrac{1}{5}.\dfrac{105}{106}$

$B=\dfrac{21}{106}$Câu trả lời: $B=\dfrac{1}{1.6}+\dfrac{1}{6.11}+\dfrac{1}{11.16}+...+\dfrac{1}{101.106}$

$B=\dfrac{1}{5}.\left(1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{16}+...+\dfrac{1}{101}-\dfrac{1}{106}\right)$

$B=\dfrac{1}{5}.\left(1-\dfrac{1}{106}\right)$

$B=\dfrac{1}{5}.\dfrac{105}{106}$

$B=\dfrac{21}{106}$