13556-356
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\(\frac{5}{3.5}\)+ \(\frac{5}{5.7}\)+ ..... + \(\frac{5}{31.33}\)
= \(\frac{5}{2}\). ( \(\frac{1}{3}\)_ \(\frac{1}{5}\)+ \(\frac{1}{5}\)_ \(\frac{1}{7}\)+.....+ \(\frac{1}{31}\)_ \(\frac{1}{33}\))
= \(\frac{5}{2}\). ( \(\frac{1}{3}\)_ \(\frac{1}{33}\))
= \(\frac{5}{2}\). \(\frac{30}{99}\)
= \(\frac{50}{66}\)
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\(\frac{3}{3.5}+\frac{3}{5.7}+...+\frac{3}{97.99}\)
\(=\frac{3}{2}\left(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\right)\)
\(=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\right)\)
\(=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{99}\right)\)
\(=\frac{3}{2}.\frac{32}{99}=\frac{16}{33}\)
Một khoảng lặng...
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Ta thấy : 1 + 9 = 10
9 + 10 = 19
Vì số thứ nhất cộng số thứ hai sẽ ra số thứ 3 Vậy X là :
10 + 19 = 29
Đáp số : 29
k mk nha
13556-356=13200
13556 - 356 = 13200
k mk nha bạn