Tính: 2/5×7+3/7×10+4/10×14+ 7/14×21+9/21×30 11/10/2021 Bởi Valerie Tính: 2/5×7+3/7×10+4/10×14+ 7/14×21+9/21×30
$\dfrac{2}{5 \times 7} + \dfrac{3}{7 \times 10} + \dfrac{4}{10 \times 14} + \dfrac{7}{14 \times 21} + \dfrac{9}{21 \times 30}$ $= \dfrac{1}{5} – \dfrac{1}{7} + \dfrac{1}{7} – \dfrac{1}{10} + \dfrac{1}{10} – \dfrac{1}{14} + \dfrac{1}{14} – \dfrac{1}{21} + \dfrac{1}{21} – \dfrac{1}{30}$ $= \dfrac{1}{5} – \dfrac{1}{30}$ $= \dfrac{5}{30}$ $= \dfrac{1}{6}$ Bình luận
Đáp án: Giải thích các bước giải: `2/5.7+3/7.10+4/10.14+ 7/14.21+9/21.30` `=1/5-1/7+1/7-1/10+1/10-1/14+1/14-1/21+1/21-1/30` `=1/5-1/30=5/30=1/6` Bình luận
$\dfrac{2}{5 \times 7} + \dfrac{3}{7 \times 10} + \dfrac{4}{10 \times 14} + \dfrac{7}{14 \times 21} + \dfrac{9}{21 \times 30}$
$= \dfrac{1}{5} – \dfrac{1}{7} + \dfrac{1}{7} – \dfrac{1}{10} + \dfrac{1}{10} – \dfrac{1}{14} + \dfrac{1}{14} – \dfrac{1}{21} + \dfrac{1}{21} – \dfrac{1}{30}$
$= \dfrac{1}{5} – \dfrac{1}{30}$
$= \dfrac{5}{30}$
$= \dfrac{1}{6}$
Đáp án:
Giải thích các bước giải:
`2/5.7+3/7.10+4/10.14+ 7/14.21+9/21.30`
`=1/5-1/7+1/7-1/10+1/10-1/14+1/14-1/21+1/21-1/30`
`=1/5-1/30=5/30=1/6`