So sánh M=15^2007+10/15^2006+10 và N = 15^2006+10/15^2005+10
Cho N=\(\dfrac{-7}{10^{2015}}\)+\(\dfrac{-15}{10^{2006}}\)và M=\(\dfrac{-15}{10^{2005}}\)+\(\dfrac{-7}{10^{2006}}\)
So sánh M và N (heo mì) TvT
Ta có :
\(N=\dfrac{-7}{10^{2005}}+\dfrac{-15}{10^{2006}}=\dfrac{-7}{10^{2005}}+\dfrac{-7}{10^{2006}}+\dfrac{-8}{10^{2006}}=-7\left(\dfrac{1}{10^{2005}}+\dfrac{1}{10^{2006}}\right)+\dfrac{-8}{10^{2006}}\)
\(M=\dfrac{-15}{10^{2005}}+\dfrac{-7}{10^{2006}}=\dfrac{-7}{10^{2005}}+\dfrac{-8}{10^{2005}}+\dfrac{-7}{10^{2006}}=-7\left(\dfrac{1}{10^{2005}}+\dfrac{1}{10^{2006}}\right)+\dfrac{-8}{10^{2005}}\)
Lại có :
\(-\dfrac{8}{10^{2006}}>\dfrac{-8}{10^{2005}}\Leftrightarrow M>N\)
N =\(\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}\)
M=\(\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
so sánh N và M
So sánh :
N = \(\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}\)và M =\(\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
\(N=\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}+\frac{-8}{10^{2006}}\)
\(M=\frac{-7}{10^{2005}}+\frac{-8}{10^{2005}}+\frac{-7}{10^{2006}}\)
Ta xét M và N, ta có: \(\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}\text{ chung}\)
Mà: \(\frac{-8}{10^{2006}}>\frac{-8}{10^{2005}}\Rightarrow M>N\)
so sánh không qua quy đồng A = -7/10^2005 + -15/10^2006 và B = -15/10^2005 + -7/10^2006
\(\hept{\begin{cases}\\\end{cases}45656.lll\hept{\begin{cases}\\\end{cases}}}\)
A = (-7/102005-7/102006) - 8/102006
B = (-7/102005-7/102006) - 8/ 102005
Vì 102006 > 102005 => 8/102006 > 8/102005 => - 8/102006 < - 8/102005 => A < B
\(A=\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}\)
\(=\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}+\frac{-8}{10^{2006}}\)
\(B=\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
\(=\frac{-7}{10^{2005}}+\frac{-8}{10^{2005}}+\frac{-7}{10^{2006}}\)
VÌ \(10^{2006}\ge10^{2005}\)
\(\Rightarrow\frac{-8}{10^{2006}}\le\frac{-8}{10^{2005}}\)
\(\Rightarrow\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}+\frac{-8}{10^{2006}}\le\frac{-7}{10^{2005}}+\frac{-8}{10^{2005}}+\frac{-7}{10^{2006}}\)
\(\Rightarrow A\le B\)
So sánh;
N=-7/10^2005 + -15/10^2006
M=-15/10^2005 + -7/10^2005
so sánh : N=\(\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}vàM=\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
Xét N ta có :
N = \(\frac{-7}{10^{2005}}\)+ \(\frac{-15}{10^{2006}}\)
N = \(\frac{-7}{10^{2005}}\)+ \(\frac{-7}{10^{2006}}\)+\(\frac{-8}{10^{2006}}\)
Xét M ta có :
M = \(\frac{-15}{10^{2005}}\)+\(\frac{-7}{10^{2006}}\)
M = \(\frac{-8}{10^{2005}}\)+\(\frac{-7}{10^{2005}}\)+ \(\frac{-7}{10^{2006}}\)
Vì \(\frac{-8}{10^{2006}}\)< \(\frac{-8}{10^{2005}}\) => N < M
ta có:M-N=\(\dfrac{-15}{10^{2005}}-\dfrac{-7}{10^{2005}}+\dfrac{-7}{10^{2006}}-\dfrac{-15}{10^{2006}}\)
=\(\dfrac{-8}{10^{2015}}\)+\(\dfrac{8}{10^{2016}}\)=8(\(\dfrac{1}{10^{2006}}-\dfrac{1}{10^{2005}}\))
Ta có:102006>102005<=>\(\dfrac{1}{10^{2006}}< \dfrac{1}{10^{2005}}\)
<=>\(\dfrac{1}{10^{2006}}-\dfrac{1}{10^{2005}}< 0\)
=>M-N<0 hay N>M
so sánh \(\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}và\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
So sánh : N = \(\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}\)và M = \(\frac{-15}{10^{2005}}+\frac{-7}{10^{2006}}\)
So sánh:
A=-7/10^2005+-15/10^2006
B=-15/10^2005+-7/10^2006