TÍNH TỔNGS =1.C22020+2.C32020+3.C42020+· · ·+2019.C20202020.A....

Câu 49. Tính tổngS =1.C

2

2020

+2.C

3

2020

+3.C

4

2020

+· · ·+2019.C

2020

2020

.A.S = 2018.2

2019

−1 B.S =2018.2

2019

+1C.S = 2018.2

2019

+2018 D.S =2020.2

2019

−1