a, A=2/3 + 2/15 + 2/35 + 2/63 +2/99 + 2/143 + 2/195 b, B=(6 4/9 + 3 7/11) – 4 4/9 20/09/2021 Bởi Maya a, A=2/3 + 2/15 + 2/35 + 2/63 +2/99 + 2/143 + 2/195 b, B=(6 4/9 + 3 7/11) – 4 4/9
`a,` `A = \frac{2}{3} + \frac{2}{15} + \frac{2}{35} + \frac{2}{63} + \frac{2}{99} + \frac{2}{143} + \frac{2}{195} ` `A = \frac{2}{1.3} + \frac{2}{3.5} + \frac{2}{5.7} + \frac{2}{7.9} + \frac{2}{9.11} + \frac{2}{11.13} + \frac{2}{13.15} ` `A = 1 – \frac{1}{3} + \frac{1}{3} – \frac{1}{5} + … + \frac{1}{13} – \frac{1}{15} ` `A = 1 – \frac{1}{15} ` `A = \frac{14}{15} ` `b,` `B = ( 6 \frac{4}{9} + 3 \frac{7}{11} ) – 4\frac{4}{9} ` `B = ( 6\frac{4}{9} – 4 \frac{4}{9} ) + 3\frac{7}{11} ` `B = 2 + 3\frac{7}{11} ` `B = 1 \frac{11}{11} + 3\frac{7}{11} ` `B = 4 \frac{18}{11} = \frac{62}{11} ` Bình luận
Đáp án: Giải thích các bước giải: $A=\dfrac{2}{3}+\dfrac{2}{15}+\dfrac{2}{35}+\dfrac{2}{63}+\dfrac{2}{99}+\dfrac{2}{143}+\dfrac{2}{195}$ $ $ $=\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}+\dfrac{2}{11.13}+\dfrac{2}{13.15}$ $ $ $=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}$ $ $ $=1-\dfrac{1}{15}$ $ $ $=\dfrac{14}{15}$ $ $ $ $ $ $ $ $ $B=(6\dfrac{4}{9}+3\dfrac{7}{11})-4\dfrac{4}{9}$ $ $ $=6+\dfrac{4}{9}+\dfrac{40}{11}-4-\dfrac{4}{9}$ $ $ $=6-4+\dfrac{40}{11}$ $ $ $=2+\dfrac{40}{11}$ $ $ $=\dfrac{22}{11}+\dfrac{40}{11}$ $ $ $=\dfrac{62}{11}$ Bình luận
`a,`
`A = \frac{2}{3} + \frac{2}{15} + \frac{2}{35} + \frac{2}{63} + \frac{2}{99} + \frac{2}{143} + \frac{2}{195} `
`A = \frac{2}{1.3} + \frac{2}{3.5} + \frac{2}{5.7} + \frac{2}{7.9} + \frac{2}{9.11} + \frac{2}{11.13} + \frac{2}{13.15} `
`A = 1 – \frac{1}{3} + \frac{1}{3} – \frac{1}{5} + … + \frac{1}{13} – \frac{1}{15} `
`A = 1 – \frac{1}{15} `
`A = \frac{14}{15} `
`b,`
`B = ( 6 \frac{4}{9} + 3 \frac{7}{11} ) – 4\frac{4}{9} `
`B = ( 6\frac{4}{9} – 4 \frac{4}{9} ) + 3\frac{7}{11} `
`B = 2 + 3\frac{7}{11} `
`B = 1 \frac{11}{11} + 3\frac{7}{11} `
`B = 4 \frac{18}{11} = \frac{62}{11} `
Đáp án:
Giải thích các bước giải:
$A=\dfrac{2}{3}+\dfrac{2}{15}+\dfrac{2}{35}+\dfrac{2}{63}+\dfrac{2}{99}+\dfrac{2}{143}+\dfrac{2}{195}$
$ $
$=\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}+\dfrac{2}{11.13}+\dfrac{2}{13.15}$
$ $
$=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{15}$
$ $
$=1-\dfrac{1}{15}$
$ $
$=\dfrac{14}{15}$
$ $
$ $
$ $
$ $
$B=(6\dfrac{4}{9}+3\dfrac{7}{11})-4\dfrac{4}{9}$
$ $
$=6+\dfrac{4}{9}+\dfrac{40}{11}-4-\dfrac{4}{9}$
$ $
$=6-4+\dfrac{40}{11}$
$ $
$=2+\dfrac{40}{11}$
$ $
$=\dfrac{22}{11}+\dfrac{40}{11}$
$ $
$=\dfrac{62}{11}$