Question

Tính nhanh:

Giúp mình nha thanks các bn ^_^

Answer 1

Ta có: \(A=\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+...+\dfrac{1}{55}+\dfrac{1}{66}\)

\(=2\left(\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+...+\dfrac{1}{110}+\dfrac{1}{132}\right)\)

\(=2\left(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{10}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{12}\right)\)

\(=2\left(\dfrac{1}{3}-\dfrac{1}{12}\right)\)

\(=2\left(\dfrac{4}{12}-\dfrac{1}{12}\right)\)

\(=2\cdot\dfrac{1}{4}=\dfrac{1}{2}\)

Answer 2

huhu giúp mình đi mn ơi T-T