Câu hỏi của Phạm Bảo Nhi

Question

1/10+1/15+1/21+....+1/105

giúp mik với ạ

Trịnh Minh Hiếu · Accepted Answer

$\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+...+\dfrac{1}{105}$

$=2\times\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+...+\dfrac{1}{210}\right)$

$=2\times\left(\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}+...+\dfrac{1}{14\times15}\right)$

$=2\times\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{14}-\dfrac{1}{15}\right)$

$=2\times\left(\dfrac{1}{4}-\dfrac{1}{15}\right)$

$=2\times\left(\dfrac{15}{60}-\dfrac{4}{60}\right)$

$=2\times\dfrac{11}{60}$

$=\dfrac{22}{60}=\dfrac{11}{30}$Câu trả lời: $\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+...+\dfrac{1}{105}$

$=2\times\left(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+...+\dfrac{1}{210}\right)$

$=2\times\left(\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}+...+\dfrac{1}{14\times15}\right)$

$=2\times\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{14}-\dfrac{1}{15}\right)$

$=2\times\left(\dfrac{1}{4}-\dfrac{1}{15}\right)$

$=2\times\left(\dfrac{15}{60}-\dfrac{4}{60}\right)$

$=2\times\dfrac{11}{60}$

$=\dfrac{22}{60}=\dfrac{11}{30}$

Phạm Bảo Nhi · Answer

cảm ơn nha

Câu trả lời: cảm ơn nha