Question

Giúp mik câu 326, làm ơn, mik cần gấp

Answer 1

Bài 326:

\(=\left(1+\dfrac{1}{2}\right)+\left(1+\dfrac{1}{6}\right)+...+\left(1+\dfrac{1}{90}\right)\\ =\left(1+1+...+1\right)+\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{9.10}\right)\\ =9+\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\\ =9+\left(1-\dfrac{1}{10}\right)=9+\dfrac{9}{10}=\dfrac{99}{10}\)