tính 1) 2/1.4 + 2/2.6 + 2/3.8 + … + 2/49.100 2) 2/1.6 + 2/2.9 + 2/3.12 + 2/4.15 + 2/5.18 + 2/6.21 03/07/2021 Bởi Audrey tính 1) 2/1.4 + 2/2.6 + 2/3.8 + … + 2/49.100 2) 2/1.6 + 2/2.9 + 2/3.12 + 2/4.15 + 2/5.18 + 2/6.21
Đáp án: `1` `2/1.4 + 2/2.6 + 2/3.8 + … + 2/49.100` `=1/1.2+1/2.3+1/3.4+…+1/49.50` `=1-1/2+1/2-1/3+1/3-1/4+…+1/49-1/50` `=1-1/50` `=49/50` `2` `A=2/1.6 + 2/2.9 + 2/3.12 + 2/4.15 + 2/5.18 + 2/6.21` `=>A/2=1/1.6+1/2.9+1/3.12+1/4.15+1/5.18+1/6.21` `=>(3A)/2=3/1.6+3/2.9+3/3.12+3/4.15+3/5.18+3/6.21` `=>(3A)/2=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7` `=>(3A)/2=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7` `=>(3A)/2=1-1/7` `=>(3A)/2=6/7` `=>3A=12/7` `=>A=4/7` Vậy biểu thức có giá trị là `4/7`. Bình luận
Đáp án + Giải thích các bước giải: 1) `2/1.4+2/2.6+2/3.8+…+2/49.100` `=1/1.2+1/2.3+1/3.4+…+1/49.50` `=1-1/2+1/2-1/3+1/3-1/4+…+1/49-1/50` `=1-1/50` `=50/50-1/50` `=49/50` 2) `2/1.6+2/2.9+2/3.12+…+2/6.21` `=2(3/3.6+3/6.9+3/9.12+…+3/18.21)` `=2(1/3-1/6+1/6-1/9+1/9-1/12+…+1/18-1/21)` `=2(1/3-1/21)` `=2(7/21-1/21)` `=2. 6/21` `=4/7` Bình luận
Đáp án:
`1`
`2/1.4 + 2/2.6 + 2/3.8 + … + 2/49.100`
`=1/1.2+1/2.3+1/3.4+…+1/49.50`
`=1-1/2+1/2-1/3+1/3-1/4+…+1/49-1/50`
`=1-1/50`
`=49/50`
`2`
`A=2/1.6 + 2/2.9 + 2/3.12 + 2/4.15 + 2/5.18 + 2/6.21`
`=>A/2=1/1.6+1/2.9+1/3.12+1/4.15+1/5.18+1/6.21`
`=>(3A)/2=3/1.6+3/2.9+3/3.12+3/4.15+3/5.18+3/6.21`
`=>(3A)/2=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7`
`=>(3A)/2=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7`
`=>(3A)/2=1-1/7`
`=>(3A)/2=6/7`
`=>3A=12/7`
`=>A=4/7`
Vậy biểu thức có giá trị là `4/7`.
Đáp án + Giải thích các bước giải:
1)
`2/1.4+2/2.6+2/3.8+…+2/49.100`
`=1/1.2+1/2.3+1/3.4+…+1/49.50`
`=1-1/2+1/2-1/3+1/3-1/4+…+1/49-1/50`
`=1-1/50`
`=50/50-1/50`
`=49/50`
2)
`2/1.6+2/2.9+2/3.12+…+2/6.21`
`=2(3/3.6+3/6.9+3/9.12+…+3/18.21)`
`=2(1/3-1/6+1/6-1/9+1/9-1/12+…+1/18-1/21)`
`=2(1/3-1/21)`
`=2(7/21-1/21)`
`=2. 6/21`
`=4/7`