Bài 1 : A. 1/8×9 + 1/9×10 + 1/10×11 + 1/11×12 + ….. + 1/50×51 B . 1/9×11 + 1/11×13 + 1/13×15 + ….. + 2/97×99 28/07/2021 Bởi Kylie Bài 1 : A. 1/8×9 + 1/9×10 + 1/10×11 + 1/11×12 + ….. + 1/50×51 B . 1/9×11 + 1/11×13 + 1/13×15 + ….. + 2/97×99
A. = `1/(8×9) + 1/(9×10) + 1/(10×11) + 1/(11×12) + ….. + 1/(50×51)` `=[(1 – 1/8) + (1/8-1/9) + (1/9 – 1/10 + (1/10 – 1/11) + (1/11 – 1/12) +….+(1/50 – 1/51)` `=1 – 1/51` `=50/51` B = `1/(9×11) + 1/(11×13) + 1/(13×15) + ….. + 2/97×2/99` `=1/2 × (1/9 – 1/11 + 1/11 – 1/14 + 1/13 – 1/15 +…+2/97 – 2/99)` `=1/2 × (1/9 – 2/99)` `=1/2 × 9/99` `=1/2 × 1/11` `=1/22` #Học tốt ! Bình luận
Đáp án: Giải thích các bước giải: A=1/8×9 + 1/9×10 + 1/10×11 + 1/11×12 + ….. + 1/50×51 A=1/8-1/9+1/9-1/10+1/10-1/11+…+1/49-1/50+1/50-1/51=1/8-1/51=51/408-8/408=43/408 B=1/9×11 + 1/11×13 + 1/13×15 + ….. + 2/97×99 2B=2/9.11 + 2/11.13 + …+2/97.99 2B=1/9-1/11+1/11-1/13+…+1/97-1/99=1/9-1/99=99/891-9/891=90/891=10/99 →B=10/99:2=10/99.1/2=10/198 Bình luận
A. = `1/(8×9) + 1/(9×10) + 1/(10×11) + 1/(11×12) + ….. + 1/(50×51)`
`=[(1 – 1/8) + (1/8-1/9) + (1/9 – 1/10 + (1/10 – 1/11) + (1/11 – 1/12) +….+(1/50 – 1/51)`
`=1 – 1/51`
`=50/51`
B = `1/(9×11) + 1/(11×13) + 1/(13×15) + ….. + 2/97×2/99`
`=1/2 × (1/9 – 1/11 + 1/11 – 1/14 + 1/13 – 1/15 +…+2/97 – 2/99)`
`=1/2 × (1/9 – 2/99)`
`=1/2 × 9/99`
`=1/2 × 1/11`
`=1/22`
#Học tốt !
Đáp án:
Giải thích các bước giải:
A=1/8×9 + 1/9×10 + 1/10×11 + 1/11×12 + ….. + 1/50×51
A=1/8-1/9+1/9-1/10+1/10-1/11+…+1/49-1/50+1/50-1/51=1/8-1/51=51/408-8/408=43/408
B=1/9×11 + 1/11×13 + 1/13×15 + ….. + 2/97×99
2B=2/9.11 + 2/11.13 + …+2/97.99
2B=1/9-1/11+1/11-1/13+…+1/97-1/99=1/9-1/99=99/891-9/891=90/891=10/99
→B=10/99:2=10/99.1/2=10/198