Question

Cho \(A=\dfrac{10^{2016}+1}{10^{2017}+1}\) và \(B=\dfrac{10^{2017}+1}{10^{2018}+1}\)

So sánh A và B

Answer 1

10a=10^2017+10/10^2017+1
10b=10^2018+10/10^2018+1

cậu tự so sánh nhé vậy là dễ rồi

Answer 2

Ta có: \(A=\dfrac{10^{2016}+1}{10^{2017}+1}\Rightarrow10A=\dfrac{10\left(10^{2016}+1\right)}{10^{2017}+1}=\dfrac{10^{2017}+10}{10^{2017}+1}\)

\(=\dfrac{10^{2017}+1+9}{10^{2017}+1}=\dfrac{10^{2017}+1}{10^{2017}+1}+\dfrac{9}{10^{2017}+1}=1+\dfrac{9}{10^{2017}+1}\)

Tương tự ta cũng có: \(10B=1+\dfrac{9}{10^{2018}+1}\)

Lại có: \(10^{2017}< 10^{2018}\Rightarrow10^{2017}+1< 10^{2018}+1\)

\(\Rightarrow\dfrac{1}{10^{2017}+1}>\dfrac{1}{10^{2018}+1}\Rightarrow\dfrac{9}{10^{2017}+1}>\dfrac{9}{10^{2018}+1}\)

\(\Rightarrow1+\dfrac{9}{10^{2017}+1}>1+\dfrac{9}{10^{2018}+1}\Rightarrow10A>10B\Rightarrow A>B\)