Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
c.\(=3\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+..+\frac{2}{99.101}\right)\)
\(=3\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\right)\)
\(=3\left(1-\frac{1}{101}\right)\)
\(=\frac{300}{101}\)
b)
\(5\left(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{26.31}\right)\)
\(5\left(1-\frac{1}{6}+...+\frac{1}{26}-\frac{1}{31}\right)\)
\(5\left(1-\frac{1}{31}\right)\)
\(=\frac{150}{31}\)
a)
\(\frac{7}{10}-\frac{7}{11}+...+\frac{7}{69}-\frac{7}{70}\)
\(=\frac{7}{10}-\frac{7}{70}\)
\(=\frac{3}{5}\)
3/4.7 + 3/7.10 + ...+ 3/73.76
=1/4 - 1/7 +1/7 - 1/10 + ... + 1/73 - 1/76
=1/4 - 1/76
=18/76
=9/38
\(\frac{3}{4x7}+\frac{3}{7x10}+.......+\frac{3}{73x76}\)
=\(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{73}-\frac{1}{76}\)
\(=\frac{1}{4}-\frac{1}{76}\)
\(=\frac{9}{38}\)
Đáp số :\(\frac{9}{38}\)
a,1/1-1/4+1/4-1/7+...+1/2008-1/2011
=(1-1/2011)+(-1/4+1/4)+...+(-1/2008+1/2008)
=1-1/2011+0+...+0
=1-1/2011
=2010/2011
cậu kia làm sai rùi
A .1/5 = 1/10.11+1/11.12+1/12.13+...+1/99,100
A . 1/5 = 1/10-1/11+1/11-1/12+...+1/99-1/100
A .1/5 = 1/10-1/100
A.1/5 = 9/199
A = 9/20
k nhé
\(A=\frac{5}{10.11}+\frac{5}{11.12}+\frac{5}{12.13}+.....+\frac{5}{99.100}\)
=\(\frac{5}{10}-\frac{5}{11}+\frac{5}{11}-\frac{5}{12}+\frac{5}{12}-\frac{5}{13}\)
=\(\frac{5}{10}-\frac{5}{100}=\frac{45}{100}\)=\(\frac{9}{20}\)
a, 1/1.2+1/1.3+...+1/99.100
= 1-1/2+1/2-1/3+1/3+...+1/99-1/100
=1-1/100
=99/100
a, \(\frac{9}{1.2}+\frac{9}{2.3}+...+\frac{9}{99.100}\)
=9.(\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{99.100}\))
= 9(1 -\(\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\))
=9(1-\(\frac{1}{100}\))
A=\(\frac{891}{100}\)
b, \(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{27.30}\)
=1-(\(\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{27}-\frac{1}{30}\))
=1-\(\frac{1}{30}\)
B=\(\frac{29}{30}\)
a) \(\dfrac{9}{1.2}+\dfrac{9}{2.3}+...+\dfrac{9}{99.100}\)
\(=9\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\right)\)
\(=9\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{99}-\dfrac{1}{100}\right)\)
\(=9\left(1-\dfrac{1}{100}\right)\)
\(=9.\dfrac{99}{100}\)
\(=\dfrac{891}{100}\)
b) \(\dfrac{3}{1.4}+\dfrac{3}{4.7}+\dfrac{3}{7.10}+...+\dfrac{3}{27.30}\)
\(=1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+...+\dfrac{1}{27}-\dfrac{1}{30}\)
\(=1-\dfrac{1}{30}\)
\(=\dfrac{29}{30}\)
A=3/4.7+3/7.10+...+3/73.76
A=1/4-1/7+1/7-1/10+1/10-1/13+....+1/73-1/76
A=1/4-1/76
A=9/38
b) B=5/10.11+5/11.12+....+5/99.100
B=5(1/10.11+1/11.12+1/12.13+...+1/99.100)
B=5(1/10-1/11+1/11-1/12+1/12-1/13+...+1/99-1/100)
B=5(1/10-1/100)
B=5.99/100
B=99/20
\(\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{73.76}\)
=\(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{73}-\frac{1}{76}\)
=\(\frac{1}{4}-\frac{1}{76}\)
=\(\frac{9}{38}\)