\(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{98.100}\)
=\(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{99}-\dfrac{1}{100}\)
=\(1-\dfrac{1}{100}\)
=\(\dfrac{99}{100}\)
Tính hợp lý: \(B=\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+...+\dfrac{2}{99.100}\)
Cho \(P=\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{2019.2021}\)
chứng tỏ rằng P<1
Tìm x biết : \(\dfrac{1}{1.3}+\dfrac{1}{3.5}+\dfrac{1}{5.7}+...+\dfrac{1}{\left(x+2\right).x}=\dfrac{20}{41}\)
Tính nhanh:
a, \(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{201\times203}\)
b, \(\dfrac{-4}{2.5}-\dfrac{4}{5.8}-\dfrac{4}{8.11}-...-\dfrac{4}{2015.2018}\)
S= 1/1.3 + 1/3.5 + 1/5.7 +................+ 1/200.202
TínhA:
A=1.3 + 3.5 + 5.7 + ...... + 45.47 + 47.49
3/1.3+3/3.5+3/5.7+.....+3/99.100
Mình cần gấp để sáng mai nộp cho cô
Chứng tỏ rằng : B = 2/3.5+2/5.7+2/7.9+...+2/97.99
A = 2/3.5 + 2/5.7 + 2/7.9 + ... + 2/95.97 + 2/97.99
