\(\frac{2005\times2007-1}{2004+2005\times2006}\)=?
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\(\frac{2006\times2007-2593}{2005\times2006+1419}=\frac{2005\times2006+2\times2006-2593}{2005\times2006+1419}\)
\(=\frac{2005\times2006+4012-2593}{2005\times2006+1419}=\frac{2005\times2006+1419}{2005\times2016+1419}=1\)
2006 * ( 2005 + 2 ) - 2593 / 2005 * 2006 + 1419
2006 * 2005 + 2006 * 2 - 2593 / 2005 * 2006 + 1419
2006 * 2005 + 4012 - 2593 / 2005 * 2006 + 1419
2006 * 2005 + 1419 / 2005 * 2006 + 1419 = 1
k cho tui nha
y=\(\frac{2006x2005-1}{2004x2006+2005}=\frac{2006x2005-1}{\left(2005-1\right)x2006+2005}=\frac{2006x2005-1}{2005x2006-2006+2005}=\frac{2006x2005-1}{2005x2006-1}=1\)
Ta có: \(\frac{2004\cdot2007+6}{2005\cdot2005+2009}=\frac{\left(2005-1\right)\cdot2007+6}{2005\cdot2005+2009}=\frac{2005\cdot2007-1\cdot2007+6}{2005\cdot2005+2009}=\frac{2005\cdot2007-2007+6}{2005\cdot2005+2009}\)
\(=\frac{\text{2005 x (2005 + 2) - 2007 + 6}}{\text{2005 x 2005 + 2009}}=\frac{\text{2005 x 2005 + 2005 x 2 - 2007 + 6}}{\text{2005 x 2005 + 2009}}=\frac{\text{2005 x 2005 + 4010 - 2007 + 6}}{\text{2005 x 2005 + 2009}}=\text{ }\frac{\text{2005 x 2005 + 2009}}{\text{2005 x 2005 + 2009}}=1\)
\(A=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{2004\cdot2005}+\frac{1}{2005\cdot2006}\)
\(A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2004}-\frac{1}{2005}+\frac{1}{2005}-\frac{1}{2006}\)
\(A=1-\frac{1}{2006}=\frac{2005}{2006}\)
\(A=\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{2005.2006}\)
\(\Rightarrow A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{2005}-\frac{1}{2006}\)
\(\Rightarrow A=1-\frac{1}{2006}\)
\(\Rightarrow A=\frac{2005}{2006}\)
\(=\frac{2005\times\left(2006+1\right)-1}{2004+2005\times2006}=\frac{2005\times2006+2005\times1-1}{2004+2005\times2006}=\frac{2005\times2006+2004}{2004+2005\times2006}=1\)