Question

Tính nhanh  :

a ) S = 2+4+6+8+.....+2018

b ) S= 10+10²+10³+...+10¹⁰⁰

c) \(S=\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{100}}\)

d) \(S=\frac{1!}{3!}+\frac{2!}{4!}+\frac{3!}{5!}+....+\frac{2018!}{2020!}\)

biết rằng : \(n!=1\times2\times3\times...\times n\)

VD : 1! = 1

2! = 2.1

3!=1.2.3

4!=1.2.3.4

! : giai thừa

Answer 1

a;b;c có những câu tương tự rồi, ko giải lại nx

d) \(S=\frac{1!}{3!}+\frac{2!}{4!}+...+\frac{2018!}{2020!}\)

\(S=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{2019.2020}\)

\(S=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2019}-\frac{1}{2020}\)

\(S=\frac{1}{2}-\frac{1}{2020}\)

b tự làm nốt nha