tính nhanh \(\frac{2014.2016-1}{2013+2014.2015}=?\)
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
=> B=2013. (1+\(\frac{1}{1+2}\) +\(\frac{1}{1+2+3}\) +...+ \(\frac{1}{1+2+3+...+2012}\))
=>B= 2013.(\(\frac{2}{2}\) + \(\frac{2}{2.3}\) +\(\frac{2}{3.4}\) +...+\(\frac{2}{2012.2013}\))
=>B= 2013.2.(\(\frac{1}{1.2}\) + \(\frac{1}{2.3}\) +\(\frac{1}{3.4}\) +...+\(\frac{1}{2012.2013}\))
=>B=4026. (1-\(\frac{1}{2}\) +\(\frac{1}{2}\) -\(\frac{1}{3}\) + ...+\(\frac{1}{2012}\) - \(\frac{1}{2013}\))
=>B=4026.(1-\(\frac{1}{2013}\))
=>B=4026.\(\frac{2012}{2013}\) => B=2.2012=4024 Vậy B=4024
![](https://rs.olm.vn/images/avt/0.png?1311)
A = 1 / 1008 + 1 / 2013 - 1 / 2016 x 2017
A = 1 / 1008 + 1 / 2013 - 1 / 2016 x 1 / 2017
B = 1 / 2014 + 1 / 2016 + 1 / 2017 + 1 / 2014 x 2016
B = 1 / 2014 + 1 / 2016 + 1 / 2017 + 1 / 2014 x 1 / 2016
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
M=2014.2015-2/2013+2013.2015=2015+2015.2013-2/2013+2013.2015=2013+2013.2015/2013+2013.2015=1
N=(-2014).20152015/20142014.2015=[(-2014):2014].(20152015:2015)/(20142014:2014).(2015:2015)=-1.10001/10001.1=-1
suy ra:M+N=1+(-1)=1-1=0
Vậy M+N=0
Bạn viết dấu "/" thành phần rồi đọc lại sẽ hiểu ngay và nhớ k cho mình nha
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1.4}{2.3}\)x\(\frac{2.5}{3.4}\)x\(\frac{3.6}{4.5}\)x.........x\(\frac{2013.2016}{2014.2015}\)=\(\frac{1.2.3....2013}{2.3.4...2014}\)x \(\frac{4.5.6....2016}{3.4.5....2015}\)
=\(\frac{1}{2014}\)x \(\frac{2016}{3}\)
=\(\frac{2016}{6042}\)= \(\frac{336}{1007}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
2014.2015-1007.30=2014.2015-2014.15=2014.(2015-15)=2014.2000=4028000
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì \(2014.2015=2014.2015\)nên \(2014.2015-1< 2014.2015\)1 đơn vi
Vì \(2015.2016=2015.2016\)nên \(2015.2016-1< 2015.2016\)1 đơn vị
Ta có :
\(1-M=1-\frac{2014.2015-1}{2014.2015}=\frac{1}{2014.2015}\)
\(1-N=1-\frac{2015.2016-1}{2015.2016}=\frac{1}{2015.2016}\)
Vì \(2015=2015\)nên \(2014.2015< 2015.2016\)
Vì \(\frac{1}{2014.2015}>\frac{1}{2015.2016}\)( do \(2014.2015< 2015.2016\))
Nên \(N>M\)
Vậy \(N>M\)
\(\frac{2014\cdot2016-1}{2013+2014\cdot2015}=\frac{2014\cdot\left(2015+1\right)-1}{2013+2014\cdot2015}=\frac{2014\cdot2015+2014-1}{2013+2014\cdot2015}=\frac{2014\cdot2015+2013}{2013+2014\cdot2015}=1\)
\(=\frac{2014.2015+2014-1}{2013+2014.2015}=\frac{2014.2015+2013}{2014.2015+2013}=1\)