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\(\frac{2006.2005-1}{2004.2006+2005}\)
\(=\frac{2006\left(2004+1\right)-1}{2004.2006+2005}\)
\(=\frac{2006.2004+2006-1}{2004.2006-2005}\)
\(=\frac{2006.2004+2005}{2004.2006+2005}=1\)
nha
a, 27.5 x 5.43 + 4.57 x 27.5
= 27.5 x ( 5.43 + 4.57 )
= 27.5 x 10
= 275
c,\(\frac{2006x2005-1}{2004x2006+2005}\)
= \(\frac{2006x\left(2004+1\right)-1}{2004x2006+2005}\)
= \(\frac{2006x2004+2006-1}{2004x2006+2005}\)
= \(\frac{2006x2004+2005}{2004x2006+2005}\)
= 1.
Mình chỉ biết từng nấy thôi.
2006 x 2005 - 1/2004 x 2006 + 2005
= 2006 x ( 2004 + 1 ) - 1/2004 x 2006 + 2005
= 2006 x 2004 + 2006 x 2005/2004 x 2006 + 2005
= 2006 x 2004 + 2005 / 2004 x 2006 + 2005
\(=\frac{2006x\left(2005+2\right)-1997}{2006x2005+2015}=\frac{2006x2005+4012-1997}{2006x2005+2015}=\frac{2006x2005+2015}{2006x2005+2015}=1\)
\(S=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(S=\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{9\times10}\)
\(S=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(S=1-\frac{1}{10}\)
\(S=\frac{9}{10}\)
\(S=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(S=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(S=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(S=1-\frac{1}{10}\)
\(S=\frac{9}{10}\)
Ta chỉ việc tách ra thôi VD ta thấy L
2006x2005 = 2006x2004+2006x 1
Vây ta sẽ có cách làm như sau :
\(\frac{2006\cdot2005-1}{2004\cdot2006+2005}\)
\(=\frac{2006\cdot2004+2006\cdot1-1}{2004\cdot2006+2005}\)
\(=\frac{2006\cdot2004+2006-1}{2006\cdot2004+2005}\)
\(=\frac{2006\cdot2004+2005}{2004\cdot2006+2005}=1\)
\(\frac{2006\cdot2005-1}{2004\cdot2006+2005}=\frac{2006\cdot\left(2004+1\right)}{2004\cdot2006+2005}=\frac{2006\cdot2004+2006\cdot1-1}{2004\cdot2006+2005}=\frac{2006\cdot2004+2005}{2004\cdot2006+2005}=1\)
\(\frac{2006\times2005-1}{2004\times2006+2005}=\frac{2006\times\left(2004+1\right)-1}{2004\times2006+2005}=\frac{2006\times2004+2006\times1-1}{2004\times2006+2005}=\frac{2006\times2004+2005}{2006\times2004+2005}=1\)
\(\frac{2006\times2005-1}{2004\times2006+2005}=\frac{2006\times\left(2004+1\right)-1}{2004\times2006+2005}=\frac{2004\times2006+2006\times1-1}{2004\times2006+2005}\)
\(=\frac{2004\times2006+2005}{2004\times2006+2005}=1\)