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cho A=\(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{98}-\frac{1}{99}\)
chứng minh rằng 0,2<A<0,4
Chứng minh rằng
a) \(\frac{1}{5}<\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{98}-\frac{1}{99}<\frac{2}{5}\)
b) \(\frac{1}{15}<\frac{1}{2}.\frac{3}{4}.\frac{5}{6}...\frac{99}{100}<\frac{1}{10}\)
cho A = \(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+......+\frac{1}{98}-\frac{1}{99}\)
chứng minh 0,2 < a < 0,4
Cho:\(A=\left(\frac{1}{1}+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{98}\right).2.3.4...98\)
Chứng minh rằng A chia hết cho 99
Cho A=\(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{98}-\frac{1}{99}\)Chứng minh 0,2<A<0,4
Cho B =\(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{98}-\frac{1}{99}\)
Chứng minh rằng 0,2 <B < 0,4
A= \(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+........+\frac{1}{98}-\frac{1}{99}\)
Chứng minh rằng: \(\frac{1}{5}\)< A < \(\frac{2}{5}\)
Bài 1:
Chứng minh rằng:
\(\frac{1}{6}< \frac{1}{5^2}+\frac{1}{6^2}+\frac{1}{7^2}+...+\frac{1}{100^2}< \frac{1}{4}\)
Bài 2:
Cho \(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{98}-\frac{1}{99}\).
CMR: \(a)A>\frac{4}{3}\); \(b)A< 2,5\)
A=\(\frac{1}{2}.\frac{3}{4}.\frac{5}{6}......\frac{97}{98}.\frac{99}{100}\)
Chứng minh 1/15 < A < 1/10