NN
5
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Các câu hỏi dưới đây có thể giống với câu hỏi trên
11 tháng 5 2016
Đặt S=1/6+1/12+1/20+1/30+1/42+1/56+1/72
=> S=1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9
=> S=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=> S=1/2-1/9
=> S=7/18
Vì 7/18<1/2
=> S<1/2
Mọi người k mik nhé, :)))
11 tháng 5 2016
1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72
= 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9
= 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + ... + 1/8-1/9
= 1/2 - 1/9
= 7/18
Bn tự so sánh vs 1/2 nha
TH
3 tháng 3 2020
\(D=\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
\(D=\frac{1}{90}-\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{8\cdot9}\right)\)
\(D=\frac{1}{90}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)\)
\(D=\frac{1}{90}-\left(1-\frac{1}{9}\right)\)
\(D=\frac{1}{90}-\frac{8}{9}=-\frac{79}{90}\)
3 tháng 3 2020
D=1/90 - 1/72 -1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
D=1/90-(1/72+1/56+1/42+1/30+1/20+1/12+1/6+1/2)
D=1/90-(1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72)
D=1/90-(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9)
D=1/90-(1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9)
D=1/90-(1/1-1/9)
D=1/90-8/9
D=(-79/90)
HM
10 tháng 4 2017
1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}\)\(+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{7}-\frac{1}{8}\)\(+\frac{1}{8}-\frac{1}{9}\)
\(=1-\frac{1}{9}\)
\(=\frac{8}{9}\)
10 tháng 4 2017
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1-1/9
=8/9
NT
3
NA
18 tháng 3 2022
\(=\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}\\ =\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}\\ =\dfrac{1}{2}-\dfrac{1}{8}=\dfrac{3}{8}\)
HH
22 tháng 7 2017
1.
A = (22.21.20 - 2.1.0) : 3
A = 9240 : 3
A = 3080
3.A = 3080 x 3
3.A = 9240
PT
6
28 tháng 4 2020
A = 1/1x2 +1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8
=1-1/2+1/2-1/3+1/3-1/4+..+1/7-1/8
=1-1/8
=7/8
A=\(\dfrac{113}{140}\)
A=\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}-\dfrac{1}{20}\)
\(=\dfrac{2-1}{1.2}+\dfrac{3-2}{2.3}+\dfrac{4-3}{3.4}+\dfrac{5-4}{4.5}+\dfrac{6-5}{5.6}+\dfrac{7-6}{6.7}-\dfrac{1}{20}\)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}-\dfrac{1}{20}\)
\(=1-\dfrac{1}{7}-\dfrac{1}{20}=1-\dfrac{27}{140}=\dfrac{113}{140}\)