tính nhanh
2155-(174+2155)+(-68+174)
2.\(\dfrac{3}{7}\left(\dfrac{2}{9}-1\dfrac{3}{7}\right)-\dfrac{5}{3}:\dfrac{1}{9}\)
\(\left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)\left(1-\dfrac{1}{4}\right)\left(1-\dfrac{1}{5}\right)\)
\(\left(\dfrac{377}{-231}-\dfrac{123}{89}+\dfrac{34}{791}\right).\left(\dfrac{1}{6}-\dfrac{1}{8}-\dfrac{1}{24}\right)\)
chứng tỏ phân số sau tối giản vs mọi số tự nhiên n\(\dfrac{n+1}{2n+3}\)
chứng tỏ B = \(1+\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{63}< 6\)
Chứng tỏ rằng : \(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{100^2}< 1\)
Chứng tỏ
\(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{100^2}< 1\)
Cho A = \(1+\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+...+\dfrac{1}{100}\)
Chứng tỏ 50 < A < 100
Cho A=\(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{9^2}\)
Chứng tỏ \(\dfrac{8}{9}>A>\dfrac{2}{5}\)
BT1: Chứng tỏ rằng: \(\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}>\dfrac{5}{6}\)
BT2: Điền vào tổng sau số còn thiếu sau đó tính tổng:
\(\dfrac{1}{5}+\dfrac{1}{45}+\dfrac{1}{117}+...+\dfrac{1}{1517}\)
Câu 1: Tìm x biết
a) \(-\dfrac{2}{3}\)\(\left(x-\dfrac{1}{4}\right)\) = \(\dfrac{1}{3}\left(2x-1\right)\) b) \(\dfrac{1}{5}.2^x+\dfrac{1}{3}.2^{x+1}=\dfrac{1}{5}.2^7+\dfrac{1}{3}.2^8\)
Câu 2: a) Cho A = \(\dfrac{1}{2}.\dfrac{3}{4}.\dfrac{5}{6}......\dfrac{9999}{10000}\)
So sánh A vs 0,01
b) Chứng tỏ rằng: \(\left[\left(1+2+3+....+n\right)-7\right]⋮̸10\)
