Question

Tính

1. S1 = 1+ ( - 2) + 3 + ( - 4) + … + ( -2020) + 2021

2. S2 = ( - 2) + 4 + ( - 6) + 8….+ ( - 2014) + 2016

S3 = 1^2 -2^2 + 3^2 - 4^2 + …. 99^2 – 100^2 +101^2

CÁC BẠN GIÚP MÌNH VỚI ! 

Answer 1

1: Ta có: \(S_1=1+\left(-2\right)+3+\left(-4\right)+...+\left(-2020\right)+2021\)

\(=\left(1-2\right)+\left(3-4\right)+...+\left(2019-2020\right)+2021\)

\(=\left(-1\right)+\left(-1\right)+...+\left(-1\right)+2021\)

\(=-1\cdot1010+2021\)

\(=-1010+2021=1011\)

2) Ta có: \(S_2=\left(-2\right)+4+\left(-6\right)+8+...+\left(-2014\right)+2016\)

\(=\left(-2+4\right)+\left(-6+8\right)+...+\left(-2014+2016\right)\)

\(=2+2+...+2\)

\(=2\cdot504=1008\)

Answer 2

Cho mình cảm ơn bạn NGUYỄN LÊ PHƯỚC THỊNH nhé