1.Tính:
a) 35-22003
b)S=1-2+2^2-2^3+....+200^2
K
Khách
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CC
1
14 tháng 1 2015
A=1002+2002+3002+...+10002
A=12.1002+22.1002+32.1002+...+102.1002
A=1002.(12+22+32+...+102)
A=10000.385
A=3850000
15 tháng 4 2022
a: \(\dfrac{1}{8}\cdot\dfrac{4}{5}:\dfrac{3}{5}=\dfrac{1}{10}\cdot\dfrac{5}{3}=\dfrac{1}{2\cdot3}=\dfrac{1}{6}\)
b: \(=\dfrac{8-3}{12}\cdot\dfrac{6}{5}=\dfrac{6}{12}=\dfrac{1}{2}\)
c: \(=\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{3}{4}\)
d: =63/21+15/21-7/21=71/21
15 tháng 4 2022
a \(\dfrac{1}{8}\times\dfrac{4}{5}\times\dfrac{10}{6}=\dfrac{1}{6}\)
b \(\left(\dfrac{8}{12}-\dfrac{3}{12}\right)\times\dfrac{6}{5}=\dfrac{5}{12}\times\dfrac{6}{5}=\dfrac{1}{2}\)
c \(\dfrac{24}{35}:\dfrac{32}{35}=\dfrac{24}{35}\times\dfrac{35}{32}=\dfrac{3}{4}\)
d \(\dfrac{63}{21}+\dfrac{15}{21}-\dfrac{7}{21}=\dfrac{71}{21}\)
ML
10 tháng 5 2016
A= 1 +\(\frac{1}{3}\)+\(\frac{1}{6}\)+ .....+ \(\frac{1}{171}\)+\(\frac{1}{190}\)
A= 1 +2.(\(\frac{1}{6}\)+\(\frac{1}{12}\)+....+\(\frac{1}{342}\)+\(\frac{1}{380}\))
A=1+ 2.(\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+....+\(\frac{1}{18.19}\)+\(\frac{1}{19.20}\))
A=1+2.(\(\frac{1}{2}\)-\(\frac{1}{3}\)+\(\frac{1}{3}\)-\(\frac{1}{4}\)+......+\(\frac{1}{18}\)-\(\frac{1}{19}\)+\(\frac{1}{19}\)-\(\frac{1}{20}\))
A=1 +2.(\(\frac{1}{2}\)-\(\frac{1}{20}\))
A=1+2.\(\frac{9}{20}\)=1+\(\frac{9}{10}\)=\(\frac{19}{10}\)
TN
10 tháng 5 2016
\(A=1+\frac{2}{6}+\frac{2}{12}+...+\frac{2}{380}\)
\(=1+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{19.20}\)
\(=1+2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{19}-\frac{1}{20}\right)\)
\(=1+2\left(\frac{1}{2}-\frac{1}{20}\right)\)
\(=1+2\times\frac{9}{20}\)
\(=1+\frac{9}{10}\)
\(=\frac{19}{10}\)
b)\(2S=2\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{20}}\right)\)
\(2S=1+\frac{1}{2}+...+\frac{1}{2^{19}}\)
\(2S-S=\left(1+\frac{1}{2}+...+\frac{1}{2^{19}}\right)-\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{20}}\right)\)
\(S=1-\frac{1}{2^{20}}\)
c)đặt A=1+2+2^2+2^3+...+2^2006+2^2007.
2A=2(1+2+2^2+2^3+...+2^2006+2^2007)
2A=2+2^2+2^3+...+2^2008
2A-A=(2+2^2+2^3+...+2^2008)-(1+2+2^2+2^3+...+2^2006+2^2007)
A=2^2008-1
2 tháng 5 2021
Giải:
a) S=52/1.6+52/6.11+52/11.16+52/16.21+52/21.26
S=5.(5.1/6+5/6.11+5/11.16+5/16.21+5/21.26)
S=5.(1/1-1/6+1/6-1/11+1/11-1/16+1/16-1/21+1/21-1/26)
S=5.(1/1-1/26)
S=5.25/26
S=125/26
b) (1-1/2).(1-1/3).(1-1/4).(1-1/5).....(1-1/19).(1-1/20)
=1/2.2/3.3/4.4/5.....18/19.19/20
=1.2.3.4.....18.19/2.3.4.5.....19.20
=1/20
Chúc bạn học tốt!
NV
Nguyễn Việt Lâm
Giáo viên
13 tháng 8 2021
\(S=a+a^3+...+a^{2n+1}\)
\(S.a^2=a^3+a^5+...+a^{2n+1}+a^{2n+3}\)
\(\Rightarrow S\left(a^2-1\right)=a^{2n+3}-a\)
\(\Rightarrow S=\dfrac{a^{2n+3}-a}{a^2-1}\)
\(S_1=1+a^2+...+a^{2n}\)
\(S_1.a^2=a^2+a^4+...+a^{2n}+a^{2n+2}\)
\(\Rightarrow S_1\left(a^2-1\right)=a^{2n+2}-1\)
\(\Rightarrow S_1=\dfrac{a^{2n+2}-1}{a^2-1}\)