\(B=\dfrac{1}{2}\left(\dfrac{2}{1\cdot2\cdot3}+\dfrac{2}{2\cdot3\cdot4}+...+\dfrac{2}{17\cdot18\cdot19}\right)\)
\(=\dfrac{1}{2}\left(\dfrac{1}{1\cdot2}-\dfrac{1}{2\cdot3}+\dfrac{1}{2\cdot3}-\dfrac{1}{3\cdot4}+...+\dfrac{1}{17\cdot18}-\dfrac{1}{18\cdot19}\right)\)
\(=\dfrac{1}{2}\left(\dfrac{1}{2}-\dfrac{1}{342}\right)=\dfrac{1}{2}\cdot\dfrac{85}{171}=\dfrac{85}{342}\)
\(M=\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{37.38.39}\right).1482+185.8\)
tính hợp lý
A= \(\dfrac{1}{1.2.3}\)+\(\dfrac{1}{2.3.4}\)+\(\dfrac{1}{3.4.5}\)+...+\(\dfrac{1}{18.19.20}\)
Cho A=\(\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+\dfrac{1}{3.4.5}+...+\dfrac{1}{2014.2015.2016}\).So sánh A với \(\dfrac{1}{4}\)
Giúp mình nha!!
Tính nhanh:
\(S=\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+...+\dfrac{1}{8.9.10}\)
tính nhanh
\(A=\frac{5}{20.22}+\frac{5}{22.24}+....+\frac{5}{79.90}\)
\(B=\frac{1}{1.2.3}+\frac{1}{2.3.4}+....+\frac{1}{18.19.20}\)
làm nhanh cho mk nha!!! bn nào trả lời đúng mk cho 2 tick
Tính:B=\(\dfrac{5^2}{2.3.4}+\dfrac{5^2}{3.4.5}+\dfrac{5^2}{4.5.6}+...+\dfrac{5^2}{48.49.50}\)
Cho \(A=\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{2022}\)
Và \(B = \dfrac{2021}{1}+\dfrac{2020}{2}+\dfrac{2019}{3}+...+\dfrac{1}{2021}\)
Tính B/A
Tìm a,b thuộc z biết:
a/7+1/4=1/b
tìm a,b ϵ Z biết: a/7-1/4=1/b
