Tính tổng A = 1/10 + 1/15 + 1/21 + ……….+ 2/240 17/10/2021 Bởi Hailey Tính tổng A = 1/10 + 1/15 + 1/21 + ……….+ 2/240
Đáp án: `A = 3/8` Giải thích các bước giải: `A = 1/10 + 1/15 + 1/21 + …+ 2/240` `A = 2/20 + 2/30 + 2/42 + … + 2/240` `A = 2/1 . ( 1/4.5 + 1/5.6 + 1/6.7 + … + 1/15.16)` `A = 2/1. (1/4 – 1/16)` `A=2/1. ( 4/16 – 1/16 )` `A =2/1. 3/16` `A = 6/16 = 3/8` Bình luận
$\dfrac{1}{10}$+$\dfrac{1}{15}$+$\dfrac{1}{21}$+…+$\dfrac{2}{240}$ =$\dfrac{2}{20}$+$\dfrac{2}{30}$+$\dfrac{2}{42}$+…+$\dfrac{2}{240}$ =$\dfrac{2}{4.5}$+ $\dfrac{2}{5.6}$+ $\dfrac{2}{6.7}$+…+ $\dfrac{2}{15.16}$=$2($$\dfrac{1}{4.5}$+ $\dfrac{1}{5.6}$+ $\dfrac{1}{6.7}$+…+ $\dfrac{1}{15.16}$$)$ =$2($$\dfrac{1}{4}$-$\dfrac{1}{5}$+$\dfrac{1}{5}$-$\dfrac{1}{6}$+$\dfrac{1}{6}$- $\dfrac{1}{7}$+…+$\dfrac{1}{15}$- $\dfrac{1}{16}$$)$ =$2($ $\dfrac{1}{4}$-$\dfrac{1}{16}$) =$2.$$\dfrac{3}{16}$ = $\dfrac{6}{16}$ Bình luận
Đáp án:
`A = 3/8`
Giải thích các bước giải:
`A = 1/10 + 1/15 + 1/21 + …+ 2/240`
`A = 2/20 + 2/30 + 2/42 + … + 2/240`
`A = 2/1 . ( 1/4.5 + 1/5.6 + 1/6.7 + … + 1/15.16)`
`A = 2/1. (1/4 – 1/16)`
`A=2/1. ( 4/16 – 1/16 )`
`A =2/1. 3/16`
`A = 6/16 = 3/8`
$\dfrac{1}{10}$+$\dfrac{1}{15}$+$\dfrac{1}{21}$+…+$\dfrac{2}{240}$
=$\dfrac{2}{20}$+$\dfrac{2}{30}$+$\dfrac{2}{42}$+…+$\dfrac{2}{240}$
=$\dfrac{2}{4.5}$+ $\dfrac{2}{5.6}$+ $\dfrac{2}{6.7}$+…+ $\dfrac{2}{15.16}$=$2($$\dfrac{1}{4.5}$+ $\dfrac{1}{5.6}$+ $\dfrac{1}{6.7}$+…+ $\dfrac{1}{15.16}$$)$
=$2($$\dfrac{1}{4}$-$\dfrac{1}{5}$+$\dfrac{1}{5}$-$\dfrac{1}{6}$+$\dfrac{1}{6}$- $\dfrac{1}{7}$+…+$\dfrac{1}{15}$- $\dfrac{1}{16}$$)$
=$2($ $\dfrac{1}{4}$-$\dfrac{1}{16}$)
=$2.$$\dfrac{3}{16}$
= $\dfrac{6}{16}$