Đáp án + Giải thích các bước giải:
b. `2/(2 . 4) + 2/(4 . 6) + ... + 2/(2020 . 2022)`
` = 1/2 - 1/4 + 1/4 - 1/6 + ... + 1/2020 - 1/2022`
` = 1/2 - 1/2022`
` = 1011/2022 - 1/2022`
` = 1010/2022 = 505/1011`
c, `2/(1.3) + 2/(3.5) + ... + 2/(2019 . 2021)`
` = 1 - 1/3 + 1/3 - 1/5 + ... + 1/2019 - 1/2021`
` = 1 - 1/2021`
` = 2021/2021 - 1/2021`
` = 2020/2021`
Bài 1: Tính
a, `4/7 + 5/13`
` = 52/91 + 35/91`
` = 87/91`
b, `2/15 + 5/7`
` = 14/105 + 75/105`
` = 89/105`
c, `41/15 xx 20/13`
` = (41 xx 4)/(13 xx 3)`
` = 164/39`
d, `3/5 + 2`
` = 3/5 + 10/5`
` = 13/5`
e, `4 - 13/4`
` = 16/4 -13/4`
` = 3/4`
f, `2 : 1/3`
` = 2 xx 3`
` = 6`
