Question

Không quy đồng phân số, hãy so sánh: A = \(\dfrac{-9}{10^{2010}}+\dfrac{-19}{10^{2011}}\)và B = \(\dfrac{-9}{10^{2011}}+\dfrac{-19}{10^{2010}}\)

Answer 1

Ta có: \(A=\dfrac{-9}{10^{2010}}+\dfrac{-19}{10^{2011}}=\dfrac{-9}{10^{2010}}+\dfrac{-9}{10^{2011}}+\dfrac{-10}{10^{2011}}\)

\(B=\dfrac{-9}{10^{2011}}+\dfrac{-19}{10^{2010}}=\dfrac{-9}{10^{2011}}+\dfrac{-9}{10^{2010}}+\dfrac{-10}{10^{2010}}\)

So sánh A với B ta thấy: \(\dfrac{-9}{10^{2010}}=\dfrac{-9}{10^{2010}};\dfrac{-9}{10^{2011}}=\dfrac{-9}{10^{2011}}\)

Mà \(\dfrac{-10}{10^{2011}}>\dfrac{-10}{10^{2010}}\)

\(\Rightarrow\) \(\dfrac{-9}{10^{2010}}+\dfrac{-9}{10^{2011}}+\dfrac{-10}{10^{2011}}>\dfrac{-9}{10^{2010}}+\dfrac{-9}{10^{2011}}+\dfrac{-10}{10^{2010}}\)

\(\Rightarrow\) \(A>B\)

Vậy A > B.