Đáp án:
A = ( 1 - 1/2) . (1 - 1/3) . (1 - 1/4) ....(1 - 1/2020) . (1 - 1/2021)
A = (2/2 - 1/2) . (3/3 - 1/3) . (4/4 - 1/4) ...... (2020/2020 - 1/2020) . (2021/2021 - 1/2021)
A = 1/2 . 2/3 . 3/4 ...... 2019/2020 . 2020/2021
A = 1/2021
Hok tốt!
Xin câu trả lời hay nhất!
#Tamthatthat