tính tổng S bằng 1/15 + 1/35 + 1/63 + ….+ 1/1443 07/08/2021 Bởi Quinn tính tổng S bằng 1/15 + 1/35 + 1/63 + ….+ 1/1443
`S= 1/15 + 1/35 + 1/63 +…+1/1443` `S= 1/3.5 + 1/5.7 + 1/7.9 +…+1/37.39` `2S= 2( 1/3.5 + 1/5.7 + 1/7.9 +…+ 1/37.39)` `2S= 2/3.5 + 2/5.7 + 2/7.9 +…+ 2/37.39` `2S= 1/3- 1/5 + 1/5 – 1/7 +…+ 1/37- 1/39` `2S= 1/3- 1/39` `2S= 4/13` `S= 4/13 : 2` `S= 4/13 . 1/2` `S= 2/13` Vậy `S= 2/13` Bình luận
Đáp án: 2/13 Giải thích các bước giải: S=1/15 + 1/35 + 1/63 + ….+ 1/1443 2S= $\frac{2}{3*5}$ +$\frac{2}{5*7}$ +$\frac{2}{7*9}$ +…. + $\frac{2}{37*39}$ 2S= $\frac{5-3}{3*5}$ +$\frac{7-5}{5*7}$ +$\frac{9-7}{7*9}$ +…. + $\frac{39-37}{37*39}$ 2S=$\frac{1}{3}$ -$\frac{1}{5}$ +$\frac{1}{5}$- $\frac{1}{7}$ +…. + $\frac{1}{37}$ -$\frac{1}{39}$ 2S= $\frac{x1}{3}$ -$\frac{1}{39}$ =$\frac{4}{13}$ S= $\frac{2}{13}$ Bình luận
`S= 1/15 + 1/35 + 1/63 +…+1/1443`
`S= 1/3.5 + 1/5.7 + 1/7.9 +…+1/37.39`
`2S= 2( 1/3.5 + 1/5.7 + 1/7.9 +…+ 1/37.39)`
`2S= 2/3.5 + 2/5.7 + 2/7.9 +…+ 2/37.39`
`2S= 1/3- 1/5 + 1/5 – 1/7 +…+ 1/37- 1/39`
`2S= 1/3- 1/39`
`2S= 4/13`
`S= 4/13 : 2`
`S= 4/13 . 1/2`
`S= 2/13`
Vậy `S= 2/13`
Đáp án:
2/13
Giải thích các bước giải:
S=1/15 + 1/35 + 1/63 + ….+ 1/1443
2S= $\frac{2}{3*5}$ +$\frac{2}{5*7}$ +$\frac{2}{7*9}$ +…. + $\frac{2}{37*39}$
2S= $\frac{5-3}{3*5}$ +$\frac{7-5}{5*7}$ +$\frac{9-7}{7*9}$ +…. + $\frac{39-37}{37*39}$
2S=$\frac{1}{3}$ -$\frac{1}{5}$ +$\frac{1}{5}$- $\frac{1}{7}$ +…. + $\frac{1}{37}$ -$\frac{1}{39}$
2S= $\frac{x1}{3}$ -$\frac{1}{39}$ =$\frac{4}{13}$
S= $\frac{2}{13}$