Tính nhanh C = (2005x2007-1)/(2004+2005x2006)
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![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{2005.2007-1}{2004+2005.2006}\)
\(=\frac{2005.\left(2006+1\right)-1}{2004+2005.2006}\)
\(=\frac{2005.2006+2005-1}{2004+2005..2006}\)
\(=\frac{2005.2006+2004}{2004+2005.2006}\)
\(=1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{2005\times2007-1}{2004+2005\times2006}\)
\(=\frac{2005\times\left(2006+1\right)-1}{2004+2005\times2006}\)
\(=\frac{2005\times2006+2005\times1-1}{2004+2005\times2006}\)
\(=\frac{2005\times2006+2005-1}{2004+2005\times2006}\)
\(=\frac{2005\times2006+2004}{2004+2005\times2006}\)
\(=1\)
_Chúc bạn học tốt_
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{2005\times2007-1}{2004+2005\times2006}\)
=\(\frac{2005\times\left(2006+1\right)-1}{2004+2005\times2006}\)
=\(\frac{2005\times2006+2005\times1-1}{2004+2005\times2006}\)
=\(\frac{2005\times2006+2005-1}{2004+2005\times2006}\)
=\(\frac{2005\times2006+2004}{2004+2005\times2006}\)
Ta thấy tử số và mẫu số giống nhau nên kết quả của biểu thức bằng 1
Li-ke cho mik nhé!
\(\frac{2005.2007-1}{2004+2005.2006}=\frac{2005.\left(2006+1\right)-1}{2004+2005.2006}=\frac{2005.2006+2005.1-1}{2004+2005.2006}=\frac{2005.2006+2004}{2004+2005.2006}=1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{2006\times2007-8}{2005\times2007+1999}\)
= \(\dfrac{\left(2005+1\right)\times2007-8}{2005\times2007+1999}\)
= \(\dfrac{2005\times2007+2007-8}{2005\times2007+1999}\)
= \(\dfrac{2005\times2007+1999}{2005\times2007+1999}\)
= 1
![](https://rs.olm.vn/images/avt/0.png?1311)
Đặt Tổng trên là A
A = 1/1.3 + 1/3.5 + 1/5.7 + .... + 1/2005.2007
2. A = 2 . ( 1/1.3 + 1/3.5 + 1/5.7 + .... + 1/2005.2007 )
2A = 2/1.3 + 2/3.5 + 2/5.7 + ..... + 2/2005.2007
2A = 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ..... + 1/2005 - 1/2007
2A = 1 - 1/2007
2A = 2006/2007
A = 2006/2007 : 2
A = 2006/4014
- Hok Tot -
\(\dfrac{1}{1\times3}+\dfrac{1}{3\times5}+\dfrac{1}{5\times7}+....+\dfrac{1}{2005\times2007}\)
= \(\dfrac{1}{2}\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{2005}-\dfrac{1}{2007}\right)\)
= \(\dfrac{1}{2}\times\left(\dfrac{1}{1}-\dfrac{1}{2007}\right)\)
= \(\dfrac{1}{2}\times\dfrac{2006}{2007}\)
= \(\dfrac{1003}{2007}\)
C=(2005x2006+2005-1)/(2004+2005x2006)=
(2005x2006+2004)/(2004+2005x2006)=1
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