tính hợp lí :
B=\(\frac{1\cdot4}{2\cdot3}+\frac{2\cdot5}{3\cdot4}+\frac{3\cdot6}{4\cdot5}+.....+\frac{98\cdot101}{99\cdot100}\)
Tính nhanh
B=\(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+...+\frac{1}{98\cdot99\cdot100}\)
Chứng tỏ \(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+...+\frac{1}{98\cdot99\cdot100}=\frac{4949}{19800}\)
\(\frac{1}{1\cdot3}-\frac{1}{2\cdot4}+\frac{1}{3\cdot5}-\frac{1}{4\cdot6}+...+\frac{1}{97\cdot99}\frac{1}{98\cdot100}\)
\(C=\left(1-\frac{2}{2\cdot3}\right)\cdot\left(1-\frac{2}{3\cdot4}\right)\cdot\left(1-\frac{2}{4\cdot5}\right)\cdot....\cdot\left(1-\frac{2}{99\cdot100}\right)\)
\(\frac{1}{1\cdot3}+\frac{1}{2\cdot4}+\frac{1}{3\cdot5}+...+\frac{1}{97\cdot99}+\frac{1}{98\cdot100}\)
Tính:
B= \(\left(1-\frac{2}{2\cdot3}\right)\) \(\left(1-\frac{2}{3\cdot4}\right)\) \(\left(1-\frac{2}{4\cdot5}\right)...\left(1-\frac{2}{99\cdot100}\right)\)
\(\frac{1}{2\cdot3}\)+\(\frac{1}{3\cdot4}\)+\(\frac{1}{4\cdot5}\)+....+\(\frac{1}{99\cdot100}\)
Tính :
\(\left(1-\frac{2}{2\cdot3}\right)\left(1-\frac{2}{3\cdot4}\right)\left(1-\frac{2}{4\cdot5}\right)\cdot...\cdot\left(1-\frac{2}{99\cdot100}\right)\)
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