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Nếu:
\(\dfrac{a}{b}< 1\Rightarrow\dfrac{a+m}{b+m}< 1\left(m\in N\right)\)
\(A=\dfrac{2005^{2005}+1}{2005^{2006}+1}< 1\)
\(A< \dfrac{2005^{2005}+1+2004}{2005^{2006}+1+2004}\Rightarrow A< \dfrac{2005^{2005}+2005}{2005^{2006}+2005}\Rightarrow A< \dfrac{2005\left(2005^{2004}+1\right)}{2005\left(2005^{2005}+1\right)}\Rightarrow A< \dfrac{2005^{2004}+1}{2005^{2005}+1}=B\)
\(A< B\)
Ta có : A = \(\dfrac{2005^{2005}+1}{2005^{2006}+1}\)
\(2005\)A = \(\dfrac{\left(2005^{2005}+1\right).2005}{2005^{2006}+1}\)
\(2005\)\(A\)= \(\dfrac{2005^{2006}+2005}{2005^{2006}+1}\)
\(2005\)\(A\)= \(\dfrac{2005^{2006}+1+2004}{2005^{2006}+1}\)
\(2005A=\dfrac{2005^{2006}+1}{2005^{2006}+1}+\dfrac{2004}{2005^{2006}+1}\)
\(2005A=1+\dfrac{2004}{2005^{2006}+1}\)
Tương tự như vậy với \(B\) ta đc
\(2005B=1+\dfrac{2004}{2005^{2005}+1}\)
Vì \(2005^{2006}+1>2005^{2005}+1\)
\(=>\) \(1+\dfrac{2004}{2005^{2006}+1}\)\(< \)\(1+\dfrac{2004}{2005^{2005}+1}\)
\(=>\)\(2005A< 2005B\)
\(=>\)\(A< B\)
Vậy \(A< B\)
Chị sử dụng cách làm lớp 7 ở câu 3 nha em
em cũng tự quy đồng và suy ra cách làm của cô giáo dạy em nha
chữ cj xấu thì mong em thông cảm
10A=\(\frac{10x\left(10^{2004}+1\right)}{10^{2005}+1}\)=
Ta có:10A=\(\frac{10^{2005}+10}{10^{2005}+1}\)=1+\(\frac{9}{10^{2005}+1}\)
10B=\(\frac{10^{2006}+10}{10^{2006}+1}\) =1+\(\frac{9}{10^{2006}+1}\)
Mà:\(\frac{9}{10^{2005}+1}\) >\(\frac{9}{10^{2006}+1}\)
Vậy:1+\(\frac{9}{10^{2005}+1}\) >1+\(\frac{9}{10^{2006}+1}\)
Vậy:A>B
cho
GIAI GIUP MINH DI
A=\(\frac{37^{2018}+5}{37^{2019}+5}\)
B=\(\frac{37^{2018}+1}{37^{2019}+1}\)
\(B=\frac{10^{2005}+1}{10^{2006}+1}<\frac{10^{2005}+1+9}{10^{2006}+1+9}=\frac{10^{2005}+10}{10^{2006}+10}=\frac{10\left(10^{2004}+1\right)}{10\left(10^{2005}+1\right)}=\frac{10^{2004}+1}{10^{2005}+1}=A\)
\(\Rightarrow\)B < A
a) Ta có : 10A = \(\frac{10\left(10^{2004}+1\right)}{10^{2005}+1}=\frac{10^{2005}+10}{10^{2005}+1}=1+\frac{9}{10^{2005}+1}\)
Lại có 10B = \(\frac{10\left(10^{2005}+1\right)}{10^{2006}+1}=\frac{10^{2006}+10}{10^{2006}+1}=1+\frac{9}{10^{2006}+1}\)
Vì \(\frac{9}{10^{2005}+1}>\frac{9}{10^{2006}+1}\Rightarrow1+\frac{9}{10^{2005}+1}>1+\frac{9}{10^{2006}+1}\)
=> 10A > 10B
=> A > B
b) Ta có A = \(\frac{20^{10}+1}{20^{10}-1}=\frac{20^{10}-1+2}{20^{10}-1}=1+\frac{2}{20^{10}-1}\)
Lại có B = \(\frac{20^{10}-1}{20^{10}-3}=\frac{20^{10}-3+2}{20^{10}-3}=1+\frac{2}{20^{10}-3}\)
Vì \(\frac{2}{20^{10}-1}< \frac{2}{20^{10}-3}\Rightarrow1+\frac{2}{20^{10}-1}< 1-\frac{2}{20^{10}-3}\)
=> A < B
\(a,\frac{20132013}{20142014}=\frac{2013.10001}{2014.10001}=\frac{2013}{2014}=1-\frac{1}{2014};\frac{131313}{141414}=\frac{13.10101}{14.10101}=\frac{13}{14}=1-\frac{1}{14}.\text{Vì: 14 bé hơn 2014 nên:}\frac{1}{14}>\frac{1}{2014}\Rightarrow\frac{20132013}{20142014}>\frac{131313}{141414}\)
\(C=2013^9+2013^9.2013=2013^9\left(2013+1\right)=2013^9.2014;D=2014^9.2014\text{ vì: 2013^9< 2014^9 nên: C bé thua D }\)
\(c,M=\frac{-7}{10^{2005}}+\frac{-15}{10^{2006}}=\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}+\frac{-8}{10^{2006}};N=\frac{-7}{10^{2005}}+\frac{-7}{10^{2006}}+\frac{-8}{10^{2005}}.Vì:10^{2006}>10^{2005}.Nên:\frac{-8}{10^{2006}}>\frac{-8}{10^{2005}}\Rightarrow M>N\)
Ta có: \(A=\frac{10^{2004}+1}{10^{2005}+1}\)
\(10A=10.\frac{10^{2004}+1}{10^{2005}+1}\)
\(=\frac{10^{2005}+10}{10^{2005}+1}\)
\(=\frac{10^{2005}+1+9}{10^{2005}+1}\)
\(=\frac{10^{2005}+1}{10^{2005}+1}+\frac{9}{10^{2005}+1}\)
\(=1+\frac{9}{10^{2005}+1}\)
Tương tự ta có: \(B=\frac{10^{2005}+1}{10^{2006}+1}\)
\(10B=10.\frac{10^{2005}+1}{10^{2006}+1}\)
\(=\frac{10^{2006}+10}{10^{2006}+1}\)
\(=\frac{10^{2006}+1+9}{10^{2006}+1}\)
\(=\frac{10^{2006}+1}{10^{2006}+1}+\frac{9}{10^{2006}+1}\)
\(=1+\frac{9}{10^{2006}+1}\)
Vì\(1+\frac{9}{10^{2005}+1}>1+\frac{9}{10^{2006}+1}\)
(Muốn so sánh 2 phân số cùng tử, phân số nào có mẫu lớn hơn thì nhỏ hơn, phân số nào có mẫu nhỏ hơn thì lớn hơn)
Nên\(A>B\)