B =\(\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+...\frac{2}{97.100}\)
=2.(\(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+...+\frac{1}{97.100}\))
3B=2.(\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{97.100}\))
3B=2.(\(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{97}-\frac{1}{100}\))
3B=2.(1-\(\frac{1}{100}\))
3B=2.\(\frac{99}{100}\)=\(\frac{99}{50}\)
=>B=\(\frac{99}{50}:3\)=\(\frac{33}{50}\)
Tick mik nha
tính tổng
a)\(\frac{9}{1.2}+\frac{9}{2.3}+\frac{9}{3.4}+...+\frac{9}{99.100}\)
b)\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{27.30}\)
c)\(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{7.10}+...+\frac{2}{93.95}\)
Tính tổng : 3^2/1.4+3^2/4.7+3^2/7.10+3^2/10.13+.............+3^2/97.100
Tính nhanh:
\(S=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.11}+\frac{3}{11.14}+\frac{3}{14.17}\)
a)6/1.4+6/4.7+6/7.10+....+6/97.100
b 4/1.3+16/3.5+36/5.7+.....+9604/97.99
c (1/1.2+1/3.4+1/5.6+...........+1/19.20)-(1/11+1/12+.....+1/20)
Chứng minh :
1.4+4.7+7.10+.......+(3n-2).(3n+1) = n.(n+1)2
giúp vs mk cần gấp
1.Tìm x, biết:
a, \(\dfrac{2}{1.4}\) + \(\dfrac{2}{4.7}\) + \(\dfrac{2}{7.10}\) + . . . + \(\dfrac{2}{x\left(x+3\right)}\) = 2018
a) (\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\)) . x =\(\frac{1}{3}\)
b) (\(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\)) : x = \(\frac{2}{3}\)
c) (\(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\)) . x = \(\frac{2}{3}\)
Mik đang cần gấp
2,Thực hiện phép tính(tính nhanh nếu có thể)
a,\(\frac{2}{3}+\frac{1}{3}\cdot\left(-\frac{2}{5}\right)\)
b,\(0,75\cdot1\frac{7}{9}-1\frac{2}{5}:\frac{-21}{20}\)
c,\(\frac{-2}{17}+\frac{15}{23}+\frac{15}{-17}-\frac{-4}{19}+\frac{8}{23}\)
d,\(2019^0\cdot\left(6-2\frac{4}{5}\right)\cdot3\frac{1}{8}-1\frac{3}{5}:25\)phần trăm
e,\(\left(\frac{7}{8}-\frac{1}{2}\right)\cdot2\frac{2}{3}-\frac{3}{7}\cdot\left(2,5^2\right)\)
B= \(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...........+\frac{1}{2012^2}\)
CMR \(\frac{1}{2}-\frac{1}{2013}< B< 1\)
