tính nhanh
\(\frac{2015.2014-1}{2013.2015+2014}\)
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2014^5 - 2015. 2014^4 + 2015.2014^3 - 2015.2014^2 + 2015.2014 + 1
Tính nhanh không sử dụng máy tính ạ
A=(2014+2015)/(2014.2015)=1/2015+1/2014 <1/2014+1/2014=2/2014=1/1007
Ta có:
\(\dfrac{2014+2015}{2015.2014}\)
\(=\dfrac{2014}{2015.2014}+\dfrac{2015}{2015.2014}\)
\(=\dfrac{1}{2015}+\dfrac{1}{2014}\)
Ta thấy:
\(\dfrac{1}{2015}+\dfrac{1}{2014}< \dfrac{1}{2014}+\dfrac{1}{2014}=\dfrac{2}{2014}=\dfrac{1}{1007}\)
\(\Rightarrow\dfrac{1}{2015}+\dfrac{1}{2014}< \dfrac{1}{1007}\)
\(\Rightarrow\dfrac{2014+2015}{2015.2014}< \dfrac{1}{1007}\)
\(=\frac{\left(2013+1\right)\cdot2015-1}{2013\cdot2015+2014}=\frac{2013\cdot2015+2015-1}{2013\cdot2015+2014}=\frac{2013\cdot2015+2014}{2013\cdot2015+2014}=1\)
\(\frac{1}{2}-\frac{1}{2016.2015}-\frac{1}{2015.2014}-...-\frac{1}{3.2}\)
\(=\frac{1}{2}-\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2015.2016}\right)\)
\(=\frac{1}{2}-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)
\(=\frac{1}{2}-\left(\frac{1}{2}-\frac{1}{2016}\right)\)
\(=\frac{1}{2}-\frac{1}{2}+\frac{1}{2016}\)
\(=\frac{1}{2016}\)
\(\frac{1}{2}-\frac{1}{2016.2015}-\frac{1}{2015.2014}-...-\frac{1}{3.2}\)
\(=\frac{1}{2}-\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{2014.2015}+\frac{1}{2015.2016}\right)\)
\(=\frac{1}{2}-\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2015}-\frac{1}{2016}\right)\)
\(=\frac{1}{2}-\left(\frac{1}{2}-\frac{1}{2016}\right)\)
\(=\frac{1}{2}-\frac{1}{2}+\frac{1}{2016}\)
\(=0+\frac{1}{2016}=\frac{1}{2016}\)
\(A=\frac{2014.2015-1}{2013.2015+2014}=\frac{2014.2015-1}{2013.2015+2015-1}=\frac{2014.2015-1}{2014.2015-1}=1\)
\(\frac{2015.2014-1}{2013.2015+2014}\)
\(=\frac{2015.2013+2015-1}{2013.2015+2014}\)
\(=\frac{2015.2013+2014}{2013.2015+2014}\)
\(=1\)
Tham khảo nhé~
\(\frac{2015\cdot2014-1}{2013\cdot2015+2014}\)
\(=\frac{2015-1}{2014}\)
\(=\frac{2014}{2014}\)
\(=1\)
\(\text{Chúc bạn học tốt ! }\)