Tính:
a) 1+\(\frac{1}{3}\)+\(\frac{1}{9}\)+\(\frac{1}{27}\)+\(\frac{1}{81}\)
b)37,52 + 4,7 x 2,3 - 9,8
Ai làm nhanh nhất,mk sẽ tick cho
Giúp mình đi hu...hu
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LL
17 tháng 4 2018
a) \(4\frac{3}{5}-\left(\frac{5}{2}-2\right)+\frac{5}{4}\)
\(=\frac{23}{5}-\frac{5}{2}+2+\frac{5}{4}\)
\(=\frac{107}{20}\)
b) \(47,31-18,27-8,27+4,6\)
\(=25,37\)
10 tháng 9 2017
\(G=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)
\(G=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^5}\)
\(3G=3+1+\frac{1}{3}+...+\frac{1}{3^4}\)
\(3G-G=\left(3+1+...+\frac{1}{3^4}\right)-\left(1+\frac{1}{3}+...+\frac{1}{3^5}\right)\)
\(2G=3-\frac{1}{3^5}\)
\(2G=3-\frac{1}{243}\)
\(2G=\frac{729}{243}-\frac{1}{243}\)
\(G=\frac{728}{243}:2\)
\(G=\frac{364}{243}\)
\(\frac{3}{1.2}+\frac{3}{2.3}+...+\frac{3}{x.\left(x+1\right)}=\frac{6042}{2015}\)
\(3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{6042}{2015}\)
\(1-\frac{1}{x+1}=\frac{6042}{2015}:3\)
\(1-\frac{1}{x-1}=\frac{2014}{2015}\)
\(\frac{1}{x-1}=1-\frac{2014}{2015}\)
\(\frac{1}{x-1}=\frac{1}{2015}\)
\(\Rightarrow x-1=2015\)
\(\Rightarrow x=2016\)
T
2
15 tháng 4 2016
A = \(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)
A = \(\frac{81}{81}+\frac{27}{81}+\frac{9}{81}+\frac{3}{81}+\frac{1}{81}\)
A = \(\frac{81+27+9+3+1}{81}\)
A = \(\frac{121}{81}\)
26 tháng 4 2017
\(1,\)
\(a,1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)
\(=\frac{81}{81}+\frac{27}{81}+\frac{9}{81}+\frac{3}{81}+\frac{1}{81}\)
\(=\frac{81+27+9+3+1}{81}\)
\(=\frac{121}{81}\)
\(=1\frac{40}{81}\)
\(b,37,25+4,7.2,3-9,8\)
\(=37,25+10,81-9,8\)
\(=38,26\)
\(2,\)
\(a,x:4,37=5,6\left(dư1,53\right)\)
\(x=5,6.4,37+1,53\)
\(\Rightarrow x=26,002\)
\(b,13,5.\left(x:5,6\right)=36,45\)
\(\left(x:5,6\right)=36,45:13,5\)
\(x:5,6=2,7\)
\(x=2,7.5,6\)
\(\Rightarrow x=15,12\)
15 tháng 7 2017
a) => 4x + 2/3 = 0 hoặc 2/3x - 1 =0
4x= -2/3 hoặc 2/3x= 1
x = -2/3 . 1/4 hoặc x = 1.3/2
x = -1/6 hoặc x = 3/2
b) x+2 / x -1 = 5/2
=> 2(x+2) = 5(x-1)
2x + 4 = 5x - 5
5x - 2x= 4+5
3x = 9
=> x= 3
15 tháng 7 2017
a) (4x+\(\frac{2}{3}\)) . ( \(\frac{2}{3}\)x-1)=0
\(\Rightarrow\)\(\orbr{\begin{cases}4x+\frac{2}{3}=0\\\frac{2}{3}x-1=0\end{cases}}\)
\(\Rightarrow\)\(\orbr{\begin{cases}x=\\x=\end{cases}}\)........
Tới đây bn tự giải nha
S
10 tháng 5 2017
Bài 1:
A = \(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{49.50}\)
= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}\)
= \(1-\frac{1}{50}=\frac{49}{50}\)
Bài 2:
Ta có: \(\frac{1}{1^2}=1;\frac{1}{2^2}< \frac{1}{1.2};\frac{1}{3^2}< \frac{1}{2.3};...;\frac{1}{50^2}< \frac{1}{49.50}\)
\(\Rightarrow A< 1+\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{49.50}\)
\(A< 1+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}=1+1-\frac{1}{50}=2-\frac{1}{50}< 2\)
Vậy A < 2
Bài 3:
\(A=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}+\frac{1}{132}\)
\(=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}\)
\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}\)
\(=\frac{1}{5}-\frac{1}{12}=\frac{7}{60}\)
Bài 4:
\(S=3+\frac{3}{2}+\frac{3}{2^2}+...+\frac{3}{2^9}\)
\(2S=6+3+\frac{3}{2}+...+\frac{3}{2^8}\)
\(2S-S=\left(6+3+\frac{3}{2}+...+\frac{3}{2^8}\right)-\left(3+\frac{3}{2}+\frac{3}{2^2}+...+\frac{3}{2^9}\right)\)
\(S=6-\frac{3}{2^9}=6-\frac{3}{512}=\frac{3069}{512}\)
10 tháng 5 2017
A=1-1/2+1/2-1/3+.............................1/49-1/50
A=1-1/50
A=49/50
a) Cho: \(A=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\)
\(\Rightarrow3A=3+1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}\)
\(\Rightarrow3A-A=3-\frac{1}{81}\)
\(\Rightarrow A=\frac{3-\frac{1}{81}}{2}\)
\(A=\frac{121}{81}\)
b) \(37,52+4,7\times2,3-9,8\)
\(=37,52+10,81-9,8\)
\(=38,53\)
Chúc bn học tốt !!!!!