Tìm y: (1/2*4 + 1/4*6 + 1/6*8 + 1/8*10) *y = 1/3 Ghi chú: mọi ngươi oi có thể thay Y thành A để ghi trước dấu bằng cho em được ko

Question

Tìm y: (1/24 + 1/46 + 1/68 + 1/810) *y = 1/3 Ghi chú: mọi ngươi oi có thể thay Y thành A để ghi trước dấu bằng cho em được ko

buigiaphong999 · Answer

`color{#8FBC8F}{~} color{#C1FFC1}{b} color{#B4EEB4}{u} color{#9BCD9B}{i} color{#698B69}{g} color{#2E8B57}{i} color{#54FF9F}{a} color{#4EEE94}{p} color{#43CD80}{h} color{#98FB98}{o} color{#008B45}{n} color{#00FF00}{g} color{#00EE00}{9} color{#00CD00}{9} color{#ADFF2F}{9} color{#228B22}{~}`
`(1/(2xx4)+1/(4xx6)+1/(6xx8)+1/(8xx10)) xx A = 1/3`
`(1/2 xx (1/2-1/4) + 1/2 xx (1/4-1/6) + 1/2xx(1/6-1/8) + 1/2xx(1/8-1/10)) xx A = 1/3`
`(1/2xx(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10)) xx A = 1/3`
`(1/2 xx (1/2-1/10)) xx A = 1/3`
`(1/2 xx 2/5) xx A = 1/3`
`1/5 xx A = 1/3`
`A = 1/3:1/5`
`A = 1/3 xx 5`
`A = 5/3`
Vậy `A=5/3`
--------------------------------
`*** 1/(n xx(n+2)) = 1/2 xx (1/n - 1/(n+2))`

nguyenphankhanhhuyen · Answer

`(1/(2xx4)+1/(4xx6)+1/(6xx8)+1/(8xx10))xxa=1/3`
`(1/2(1/2 -1/4 + 1/4 -1/6 + 1/6 -1/8+1/8-1/10))xxa=1/3`
`(1/2(1/2-1/10))xxa=1/3`
`(1/2 . 2/5)xxa=1/3`
`1/5xxa=1/3`
`a=1/3:1/5`
`a=1/3. 5`
`a=5/3`