tính giá trị biểu thức
Q=\(\frac{1}{1\cdot3}\)-\(\frac{1}{2\cdot4}\)+\(\frac{1}{3\cdot5}\)-\(\frac{1}{4\cdot6}+......+\frac{1}{97\cdot99}-\frac{1}{98\cdot100}\)
\(\frac{1}{1\cdot3}+\frac{1}{2\cdot4}+\frac{1}{3\cdot5}+...+\frac{1}{97\cdot99}+\frac{1}{98\cdot100}\)
Chứng tỏ \(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+...+\frac{1}{98\cdot99\cdot100}=\frac{4949}{19800}\)
Tính nhanh
B=\(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+\frac{1}{3\cdot4\cdot5}+...+\frac{1}{98\cdot99\cdot100}\)
tính hợp lí :
B=\(\frac{1\cdot4}{2\cdot3}+\frac{2\cdot5}{3\cdot4}+\frac{3\cdot6}{4\cdot5}+.....+\frac{98\cdot101}{99\cdot100}\)
Bài 4 : Tính bằng cách hợp lí nếu có thể
A=0.5+\(\frac{1}{3}\)+0.4+\(\frac{5}{7}\)+\(\frac{1}{6}\)-\(\frac{4}{35}\)
B=-66(\(\frac{1}{2}\)-\(\frac{1}{3}+\frac{1}{11}\))+124*(-37)+63*(-124)
C=\(\frac{8}{9}+\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}-\frac{1}{56}-\frac{1}{72}\)
D=\(\frac{1}{1\cdot3}-\frac{1}{2\cdot4}+\frac{1}{3\cdot5}-\frac{1}{4\cdot6}+....+\frac{1}{97\cdot99}-\frac{1}{98\cdot100}\)
E=\(\frac{\frac{1}{3}-\frac{1}{7}-\frac{1}{13}}{\frac{2}{3}-\frac{2}{7}-\frac{2}{13}}\)*\(\frac{\frac{1}{3}-0.25+0.2}{1\frac{1}{6}-0.875+0.7}+\frac{6}{7}\)
cho \(B=\frac{2^2}{1\cdot3}+\frac{3^2}{2\cdot4}+\frac{4^2}{3\cdot5}+...+\frac{99^2}{98\cdot100}\). Tìm phần nguyên của B
\(\frac{1}{10\cdot9}-\frac{1}{9\cdot8}-\frac{1}{8\cdot7}-\frac{1}{7\cdot6}-\frac{1}{6\cdot5}-\frac{1}{5\cdot4}-\frac{1}{4\cdot3}-\frac{1}{3\cdot2}-\frac{1}{2\cdot1}\)
Tính tổng:\(S=\frac{1}{1\cdot3}-\frac{1}{2\cdot4}+\frac{1}{3\cdot5}-\frac{1}{4\cdot6}+\frac{1}{5\cdot7}-\frac{1}{6\cdot8}+\frac{1}{7\cdot9}-\frac{1}{8\cdot10}\)