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Ta có:
\(A=1+2.6+3.6^2+4.6^3+...+100.6^{99}\)
=> \(6A=6+2.6^2+3.6^3+....+99.6^{99}+100.6^{100}\)
=> A - 6A = \(1+6+6^2+6^3+...+6^{99}-100.6^{100}\)
=> \(-5A=1+6+6^2+...+6^{99}-100.6^{100}\)
Đặt: \(B=1+6+6^2+...+6^{99}\)
=> \(6B=6+6^2+6^3+...+6^{100}\)
=> 6 B - B = \(6^{100}-1\)
=> B = \(\frac{6^{100}-1}{5}\)
=> \(-5A=\frac{6^{100}-1}{5}-100.6^{100}\)
=> \(A=\frac{499.6^{100}+1}{25}\)
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a: \(A=\dfrac{3^3\cdot2^3+3^3\cdot2^2+3^3\cdot1}{-13}=\dfrac{27\left(2^3+2^2+1\right)}{-13}=-27\)
b: \(B=\dfrac{2\cdot2^{12}\cdot3^6+2^{11}\cdot3^9}{2^3\cdot2^7\cdot3^7+2^7\cdot2^3\cdot5\cdot3^8}\)
\(=\dfrac{2^{13}\cdot3^6+2^{11}\cdot3^9}{2^{10}\cdot3^7+2^{10}\cdot5\cdot3^8}\)
\(=\dfrac{2^{11}\cdot3^6\left(2^2+3^3\right)}{2^{10}\cdot3^7\left(1+5\cdot3\right)}=\dfrac{2}{3}\cdot\dfrac{4+27}{1+15}=\dfrac{2}{3}\cdot\dfrac{31}{16}=\dfrac{31}{24}\)
c: \(C=\dfrac{5\cdot2^{30}\cdot3^{18}-2^{29}\cdot3^{20}}{5\cdot2^{35}\cdot3^{19}-7\cdot2^{29}\cdot3^{18}}\)
\(=\dfrac{2^{29}\cdot3^{18}\left(5\cdot2-3^2\right)}{2^{29}\cdot3^{18}\left(5\cdot2^6-7\right)}=\dfrac{10-9}{5\cdot64-7}=\dfrac{1}{313}\)
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Bài 1:
a) Ta có: \(\dfrac{7^4\cdot3-7^3}{7^4\cdot6-7^3\cdot2}\)
\(=\dfrac{7^3\cdot\left(7\cdot3-1\right)}{7^3\cdot2\left(7\cdot3-1\right)}\)
\(=\dfrac{1}{2}\)
c) Ta có: \(E=1+\dfrac{1}{3}+\dfrac{1}{3^2}+...+\dfrac{1}{3^{100}}\)
\(\Leftrightarrow\dfrac{1}{3}\cdot E=\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{101}}\)
\(\Leftrightarrow E-\dfrac{1}{3}\cdot E=1+\dfrac{1}{3}+\dfrac{1}{3^2}+...+\dfrac{1}{3^{100}}-\left(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{101}}\right)\)
\(\Leftrightarrow E\cdot\dfrac{2}{3}=1-\dfrac{1}{3^{101}}\)
\(\Leftrightarrow E=\dfrac{3-\dfrac{3}{3^{101}}}{2}=\dfrac{1-\dfrac{1}{3^{100}}}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\frac{2\cdot\left(2^3\right)^4\cdot\left(3^3\right)^8+2^2\cdot\left(2\cdot3\right)^9}{2^7\cdot6^7+2^7\cdot\left(2^3\cdot5\right).\left(3^2\right)^4}\)
\(A=\frac{2\cdot2^{12}\cdot3^{24}+2^2\cdot\left(2\cdot3\right)^9}{12^7+2^7\cdot\left(2^3\cdot5\right)\cdot3^8}\)
Đến đó thì bí
nhào vô $$$$$$$$$$ cho money
Trả lời :
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^_^