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\(B=\frac{1+2+2^2+2^3+...+2^{2008}}{1-2^{2009}}\)

Đặt: \(A=1+2+2^2+2^3+....+2^{2008}\)

\(\Rightarrow2A=2+2^2+2^3+2^4+...+2^{2009}\)

\(\Rightarrow2A-A=\left(2+2^2+2^3+2^4+...+2^{2009}\right)-\left(1+2+2^2+2^3+....+2^{2008}\right)\)

\(\Rightarrow2^{2009}-1\)

\(\Rightarrow B=\frac{2^{2009}-1}{1-2^{2009}}\)

Đặt \(A=1+2+2^2+2^3+...+2^{2008}\)

\(\Rightarrow2A=2+2^2+2^3+2^4...+2^{2009}\)

\(\Rightarrow2A-A=2+2^2+2^3+2^4...+2^{2009}-1-2-2^2-2^3-...-2^{2008}\)

\(\Rightarrow A=2^{2009}-1\)

\(\Rightarrow B=\frac{2^{2009}-1}{1-2^{2009}}=\frac{-1\left(1-2^{2009}\right)}{1-2^{2009}}=-1\)

\(9\times\left(x-3\right)-3\times\left(1-x\right)=23\)

\(\Rightarrow9\times x-27-3+3\times x=23\)

\(\Rightarrow12\times x-30=23\)

\(\Rightarrow12\times x=53\)

\(\Rightarrow x=\frac{53}{12}\)

x=\(\frac{53}{12}\)

2x-51:17=5

2x-51     =5.17

2x-51     =85

2x          =85+51

2x          =136

x            =136:2

x            68

k mik nha

=240:8+25x4+7x10

=30+100+70

=200

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