Làm ơn, nhanh giúp em Tính 3/4×6+3/48+3/80+…+3/624 04/10/2021 Bởi Margaret Làm ơn, nhanh giúp em Tính 3/4×6+3/48+3/80+…+3/624
$\dfrac{3}{4.6} + \dfrac{3}{48} + \dfrac{3}{80} + …. + \dfrac{3}{624}$ $=\dfrac{3}{2}.( \dfrac{2}{4.6} + \dfrac{2}{6.8} + \dfrac{2}{8.10} + …. + \dfrac{2}{24.26})$ $= \dfrac{3}{2}.(\dfrac{1}{4} – \dfrac{1}{6} + \dfrac{1}{6} – \dfrac{1}{8} + \dfrac{1}{8} – \dfrac{1}{10} + ….. + \dfrac{1}{24} – \dfrac{1}{26})$ $= \dfrac{3}{2}.(\dfrac{1}{4} – \dfrac{1}{26})$ $= \dfrac{3}{2}.\dfrac{11}{52}$ $= \dfrac{33}{104}$ Bình luận
Đặt `A=3/4.6+3/48+3/80+…+3/624` `⇒A=3/4.6+3/6.8+3/8.10+…+3/24.26` `⇒2/3A=2/4.6+2/6.8+2/8.10+…+2/24.26` `⇒2/3A=2/4.6+2/6.8+2/8.10+…+2/24.26` `⇒2/3A=1/4-1/6+1/6-1/8+1/8-1/10+…+1/24-1/26` `⇒2/3A=1/4-1/26` `⇒2/3A=11/52` `⇒A=33/104` Bình luận
$\dfrac{3}{4.6} + \dfrac{3}{48} + \dfrac{3}{80} + …. + \dfrac{3}{624}$
$=\dfrac{3}{2}.( \dfrac{2}{4.6} + \dfrac{2}{6.8} + \dfrac{2}{8.10} + …. + \dfrac{2}{24.26})$
$= \dfrac{3}{2}.(\dfrac{1}{4} – \dfrac{1}{6} + \dfrac{1}{6} – \dfrac{1}{8} + \dfrac{1}{8} – \dfrac{1}{10} + ….. + \dfrac{1}{24} – \dfrac{1}{26})$
$= \dfrac{3}{2}.(\dfrac{1}{4} – \dfrac{1}{26})$
$= \dfrac{3}{2}.\dfrac{11}{52}$
$= \dfrac{33}{104}$
Đặt `A=3/4.6+3/48+3/80+…+3/624`
`⇒A=3/4.6+3/6.8+3/8.10+…+3/24.26`
`⇒2/3A=2/4.6+2/6.8+2/8.10+…+2/24.26`
`⇒2/3A=2/4.6+2/6.8+2/8.10+…+2/24.26`
`⇒2/3A=1/4-1/6+1/6-1/8+1/8-1/10+…+1/24-1/26`
`⇒2/3A=1/4-1/26`
`⇒2/3A=11/52`
`⇒A=33/104`