Rút gọn 1/30+1/42+1/56+1/72+‧‧‧‧‧‧+1/9900 13/08/2021 Bởi Margaret Rút gọn 1/30+1/42+1/56+1/72+‧‧‧‧‧‧+1/9900
Đáp án: `1/{30}+1/{42}+1/{56}+1/{72}+‧‧‧‧‧‧+1/{9900}` `=1/{5.6}+1/{6.7}+1/{7.8}+1/{8.9}+…+1/{99.100}` `=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-…+1/{99}-1/{100}` `=1/5-1/{100}` `=19/{100}` Bình luận
Đáp án: Ta có : $\dfrac{1}{30}$ + $\dfrac{1}{42}$ + $\dfrac{1}{56}$ + …. + $\dfrac{1}{9900}$ = $\dfrac{1}{5.6}$ + $\dfrac{1}{6.7}$ + $\dfrac{1}{7.8}$ + …. + $\dfrac{1}{99.100}$ = $\dfrac{1}{5}$ – $\dfrac{1}{6}$ + $\dfrac{1}{6}$ – $\dfrac{1}{7}$ + …. + $\dfrac{1}{99}$ – $\dfrac{1}{100}$ = $\dfrac{1}{5}$ – $\dfrac{1}{100}$ = $\dfrac{19}{100}$ Giải thích các bước giải: Bình luận
Đáp án:
`1/{30}+1/{42}+1/{56}+1/{72}+‧‧‧‧‧‧+1/{9900}`
`=1/{5.6}+1/{6.7}+1/{7.8}+1/{8.9}+…+1/{99.100}`
`=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-…+1/{99}-1/{100}`
`=1/5-1/{100}`
`=19/{100}`
Đáp án:
Ta có :
$\dfrac{1}{30}$ + $\dfrac{1}{42}$ + $\dfrac{1}{56}$ + …. + $\dfrac{1}{9900}$
= $\dfrac{1}{5.6}$ + $\dfrac{1}{6.7}$ + $\dfrac{1}{7.8}$ + …. + $\dfrac{1}{99.100}$
= $\dfrac{1}{5}$ – $\dfrac{1}{6}$ + $\dfrac{1}{6}$ – $\dfrac{1}{7}$ + …. + $\dfrac{1}{99}$ – $\dfrac{1}{100}$
= $\dfrac{1}{5}$ – $\dfrac{1}{100}$
= $\dfrac{19}{100}$
Giải thích các bước giải: