Question

1.Thực hiện phép tính:

a, \(\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{2016}+\dfrac{1}{2017}\)

b, 2016+\(\dfrac{2015}{2}+\dfrac{2014}{3}+...+\dfrac{2}{2015}+\dfrac{1}{2016}\)

2.a. Tìm các số tự nhiên x, y. sao cho (2x+1)(y-5)=12

b.Tìm số tự nhiên sao cho 4n-5 chia hết cho 2n-1

Answer 1

1,

đặt A= \(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+....+\(\dfrac{1}{2016}\)+\(\dfrac{1}{2017}\)

2A=1+\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+....+\(\dfrac{1}{2015}\)+\(\dfrac{1}{2016}\)

2A-A=(1+\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+....+\(\dfrac{1}{2015}\)+\(\dfrac{1}{2016}\))-(\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+....+\(\dfrac{1}{2016}\)+\(\dfrac{1}{2017}\))

A=1-\(\dfrac{1}{2017}\)

A=\(\dfrac{2016}{2017}\)

vậy A=\(\dfrac{2016}{2017}\)

Answer 2

Bạn ơi hnhf như đề bài phải là tính \(^{\dfrac{a}{b}}\)chứ k thì làm sao mak tính đc phần b