2/6 + 2/12 + 2/20 + ….+ 2/x(x+1) = 4/5 giúp mk vs ak 08/08/2021 Bởi Josephine 2/6 + 2/12 + 2/20 + ….+ 2/x(x+1) = 4/5 giúp mk vs ak
`2/6 + 2/12 + 2/20 + ….+ 2/[x(x+1)] = 4/5``2(1/6+1/12+1/20+…+1/[x(x+1)])=4/5``2(1/2.3+1/3.4+1/4.5+…+1/[x(x+1)])=4/5``2(1/2-1/3+1/3-1/4+1/4-1/5+…+1/x-1/[x+1])=4/5``2(1/2-1/[x+1])=4/5``1/2-1/[x+1]=4/5:2``1/2-1/[x+1]=4/5. 1/2``1/2-1/[x+1]=2/5``1/[x+1]=1/2-2/5``1/[x+1]=5/10-4/10``1/[x+1]=1/10``x+1=10``x=10-1``x=9`Vậy `x=9` Bình luận
Đáp án:+Giải thích các bước giải: – Ta có: `2/6` + `2/12` + `2/20` +……..+ `2/x.(x+1)` = `4/5` ⇒ `2/2.3` + `2/3.4` + `2/4.5` +……..+ `2/x.(x+1)` = `4/5` ⇒ 2. [`1/2.3` + `1/3.4` + `1/4.5` +……..+ `1/x.(x+1)`] = `4/5` ⇒ 2. (`1/2` – `1/3` + `1/3` – `1/4`+ `1/4` – `1/5` +……..+ `1/x` – $\frac{1}{x+1}$ ) = `4/5` ⇒ 2. ( `1/2` – `1/x+1` ) = `4/5` ⇒ 1 – `2/x+1` = `4/5` ⇒ `2/x+1` = 1- `4/5` ⇒ `2/x+1` = `1/5` ⇒ (x+1) . 1 = 2 . 5 ⇒ x + 1 = 10 ⇒ x = 10 -1 ⇒ x = 9 Vậy x = 9 Xin CTLHN kèm 5 sao Bình luận
`2/6 + 2/12 + 2/20 + ….+ 2/[x(x+1)] = 4/5`
`2(1/6+1/12+1/20+…+1/[x(x+1)])=4/5`
`2(1/2.3+1/3.4+1/4.5+…+1/[x(x+1)])=4/5`
`2(1/2-1/3+1/3-1/4+1/4-1/5+…+1/x-1/[x+1])=4/5`
`2(1/2-1/[x+1])=4/5`
`1/2-1/[x+1]=4/5:2`
`1/2-1/[x+1]=4/5. 1/2`
`1/2-1/[x+1]=2/5`
`1/[x+1]=1/2-2/5`
`1/[x+1]=5/10-4/10`
`1/[x+1]=1/10`
`x+1=10`
`x=10-1`
`x=9`
Vậy `x=9`
Đáp án:+Giải thích các bước giải:
– Ta có: `2/6` + `2/12` + `2/20` +……..+ `2/x.(x+1)` = `4/5`
⇒ `2/2.3` + `2/3.4` + `2/4.5` +……..+ `2/x.(x+1)` = `4/5`
⇒ 2. [`1/2.3` + `1/3.4` + `1/4.5` +……..+ `1/x.(x+1)`] = `4/5`
⇒ 2. (`1/2` – `1/3` + `1/3` – `1/4`+ `1/4` – `1/5` +……..+ `1/x` – $\frac{1}{x+1}$ ) = `4/5`
⇒ 2. ( `1/2` – `1/x+1` ) = `4/5`
⇒ 1 – `2/x+1` = `4/5`
⇒ `2/x+1` = 1- `4/5`
⇒ `2/x+1` = `1/5`
⇒ (x+1) . 1 = 2 . 5
⇒ x + 1 = 10
⇒ x = 10 -1
⇒ x = 9
Vậy x = 9
Xin CTLHN kèm 5 sao