Đáp án `+`Giải thích các bước giải:
` E = (1-1/2)(1-1/3)....(1-1/2021) `
`= (2/2-1/2)(3/3-1/3)......(2021/2021 - 1/2021) `
` = 1/2 . 2/3 . 3/4 ......2020/2021 `
`= (1.2.3.....2020)/(2.3.4....2021) `
`= 1/2021 `
` F = (1-1/3)(1-1/6)....(1-1/780) `
`= (3/3-1/3)(6/6-1/6)....(780/780-1/780)`
`= 2/3 .5/6 ... 779/780 `
`= 4/6 . 10/12 .... 1558/1560`
`= (1.4)/(2.3) . (2.5)/(3.4) .... (38.41)/(39.40) `
`= ((1.2.3....38).(4.5.6....41))/((2.3.4....39).(3.4.5....40)) `
`= (1.41)/(39.3 ) = 41/117 `
` G = (1+1/(1.3))(1+1/(2.4).......(1+1/(98.100)) `
`= 4/(1.3) .9/(2.4) ..... (10000)/(98.100) `
`= 2^2/(1.3) . (3^2)/(2.4) ..... (100^2)/(98.100) `
`= (2.2.3.3.....100.100)/(1.3.2.4....98.100) `
` = 99/50 `