2^2010-2^2009-2^2008-2^2007-....-2-1
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\(C=\frac{\frac{1}{2008}-\frac{1}{2009}-\frac{1}{2010}}{\frac{5}{2008}-\frac{5}{2009}-\frac{5}{2010}}+\frac{\frac{2}{2007}-\frac{2}{2008}-\frac{2}{2009}}{\frac{3}{2007}-\frac{3}{2008}-\frac{3}{2009}}\)
\(=\frac{\frac{1}{2008}-\frac{1}{2009}-\frac{1}{2010}}{5.\left(\frac{1}{2008}-\frac{1}{2009}-\frac{1}{2010}\right)}+\frac{2.\left(\frac{1}{2007}-\frac{1}{2008}-\frac{1}{2009}\right)}{3.\left(\frac{1}{2007}-\frac{1}{2008}-\frac{1}{2009}\right)}\)
\(=\frac{1}{5}+\frac{2}{3}\)
\(=\frac{13}{15}\)
Đặt :
\(A=2^{2009}+2^{2008}+......+2+1\)
\(\Leftrightarrow2A=2^{2010}+2^{2009}+......+2^2+2\)
\(\Leftrightarrow2A-A=\left(2^{2010}+2^{2009}+.....+2\right)-\left(2^{2009}+2^{2008}+.....+2+1\right)\)
\(\Leftrightarrow A=2^{2010}-1\)
\(\Leftrightarrow2^{2010}-A=2^{2010}-\left(2^{2010}-1\right)=2^{2010}-2^{2010}+1=1\)
Vậy..
Đặt A=\(2^{2010}-\left(2^{2009}+2^{2008}+2^{2007}+...+2^1+2^0\right)\)
Khi đó:\(A=2^{2010}-2^{2009}-2^{2008}-...-2^1-2^0\\ \Rightarrow2A=2^{2011}-2^{2010}-2^{2009}-...-2^1\\ 2A-A=2^{2011}-2^{2010}-2^{2009}-...-2^1-\left(2^{2010}-2^{2009}-....-2^1-2^0\right)\\ A=2^{2011}-2^{2010}-...-2^1+2^{2010}+2^{2009}+...+2^0\\ A=2^{2011}-2.2^{2010}+2^0\\ A=1\)Vậy A=1
(2010-2009+2008-2007+......+2-1): (-5)
=[(2010-2009)+(2008-2007)+...+(2-1)] :(-5)
=(1+1+...+ 1+1) :(-5)
=(1.1005) :(-5)
= 1005:(-5)
= -201
Bài làm:
\(A=1-2+3-4+5-...-2008+2009\)
\(A=\left(1-2\right)+\left(3-4\right)+\left(5-6\right)+...+\left(2007-2008\right)+2009\)
\(A=-1-1-1-...-1+2009\)(1004 số -1)
\(A=-1004+2009=1005\)
\(B=1+2-3-4+5+6-7-...-2007-2008+2009+2010\)
\(B=1+\left(2-3-4+5\right)+\left(6-7-8+9\right)+...+\left(2006-2007-2008+2009\right)+2010\)
\(B=1+0+0+...+0+2010\)
\(B=2011\)
Học tốt!!!!