Toán so sánh S BIẾT rằng : S=1+1/3+1/6+1/10+…….+1/45 [giải theo cán cấp 1] 08/09/2021 By Hadley so sánh S BIẾT rằng : S=1+1/3+1/6+1/10+…….+1/45 [giải theo cán cấp 1]
`S = 1 + 1/3 + 1/6 + 1/10 + … + 1/45` `S = 2/2 + 2/6 + 2/12 + 2/20 + … + 1/90` `S = 2 . `($\dfrac{1}{1.2}$` + `$\dfrac{1}{2.3}$` + `$\dfrac{1}{3.4}$` + `$\dfrac{1}{4.5}` + … +` $\dfrac{1}{9.10}$`)` `S = 2 . (1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/9 – 1/10)` `S = 2 . (1 – 1/10)` `S = 2 . 9/10` `S = 9/5` `Vì` `9/5 < 2` `=> S < 2` Trả lời
S=1+1/3+1/6+1/10+…….+1/45 1/2×S=1/2+1/6+1/12+1/20+……+1/90 1/2×S=1/1×2+1/2×3+1/3×4+1/4×5+……+1/9×10 1/2×S=1-1/2+1/2-1/3+1/3-1/4+1/4-…….-1/9+1/9-1/10 1/2×S=1-1/10 1/2×S=9/10 S=9/10:1/2 S=9/5 xin hay nhất ạ Trả lời
`S = 1 + 1/3 + 1/6 + 1/10 + … + 1/45`
`S = 2/2 + 2/6 + 2/12 + 2/20 + … + 1/90`
`S = 2 . `($\dfrac{1}{1.2}$` + `$\dfrac{1}{2.3}$` + `$\dfrac{1}{3.4}$` + `$\dfrac{1}{4.5}` + … +` $\dfrac{1}{9.10}$`)`
`S = 2 . (1 – 1/2 + 1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + … + 1/9 – 1/10)`
`S = 2 . (1 – 1/10)`
`S = 2 . 9/10`
`S = 9/5`
`Vì` `9/5 < 2`
`=> S < 2`
S=1+1/3+1/6+1/10+…….+1/45
1/2×S=1/2+1/6+1/12+1/20+……+1/90
1/2×S=1/1×2+1/2×3+1/3×4+1/4×5+……+1/9×10
1/2×S=1-1/2+1/2-1/3+1/3-1/4+1/4-…….-1/9+1/9-1/10
1/2×S=1-1/10
1/2×S=9/10
S=9/10:1/2
S=9/5
xin hay nhất ạ