Toán Tính nhanh tổng sau: S = 1/3 + 1/15 + 1/35 + 1/63 +………+1/120 02/12/2021 By Iris Tính nhanh tổng sau: S = 1/3 + 1/15 + 1/35 + 1/63 +………+1/120
Đáp án: Giải thích các bước giải: S = 1/3 + 1/15 + 1/35 + 1/63 + 1/99 + 1/143 + 1/195 2S = 2/(1 x 3) + 2/(3 x 5) + 2/(5 x 7) + 2/(7 x 9) + 2/(9 x 11) + 2/(11 x 13) + 2/(13 x 15) 2S = 1/1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13 + 1/13 – 1/15 2S = 1/1 – 1/15 2S = 14/15 S = 14/15 : 2 S = 7/15 Vậy S = 7/15 Trả lời
`S = 1/3 + 1/15 + 1/35 + 1/63 +………+1/120` `2S=1/(1 × 3) + 1/(3 × 5) + 1/(5 × 7) + 1/(7 × 9) + 1/(9 × 11) + 1/(11 × 13) + 1/(13 × 15)` `2S=1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13 + 1/13 – 1/15` `2S = 1 – 1/15` `2S = 14/15` `S = 7/15` Vây `S = {7/15}` Trả lời
Đáp án:
Giải thích các bước giải:
S = 1/3 + 1/15 + 1/35 + 1/63 + 1/99 + 1/143 + 1/195
2S = 2/(1 x 3) + 2/(3 x 5) + 2/(5 x 7) + 2/(7 x 9) + 2/(9 x 11) + 2/(11 x 13) + 2/(13 x 15)
2S = 1/1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13 + 1/13 – 1/15
2S = 1/1 – 1/15
2S = 14/15
S = 14/15 : 2
S = 7/15
Vậy S = 7/15
`S = 1/3 + 1/15 + 1/35 + 1/63 +………+1/120`
`2S=1/(1 × 3) + 1/(3 × 5) + 1/(5 × 7) + 1/(7 × 9) + 1/(9 × 11) + 1/(11 × 13) + 1/(13 × 15)`
`2S=1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13 + 1/13 – 1/15`
`2S = 1 – 1/15`
`2S = 14/15`
`S = 7/15`
Vây `S = {7/15}`