A = 1111111111 – 22222=1111x10001-2x1111=1111(10001-2)=1111x9999=1111.3.3333=3333x3333=3333^2
=>..............
Ta có
\(1111111111=\frac{9999999999}{9}=\frac{9999999999+1-1}{9}=\frac{10^{10}-1}{9}.\)
\(22222=2.11111=\frac{2.99999}{9}=\frac{2\left(99999+1-1\right)}{9}=\frac{2\left(10^5-1\right)}{9}\)
\(\Rightarrow A=\frac{10^{10}}{9}-\frac{1}{9}-2.\frac{10^5}{9}+\frac{2}{9}=\)
\(=\left(\frac{10^5}{3}\right)^2-2.\frac{10^5}{3}.\frac{1}{3}+\left(\frac{1}{3}\right)^2=\left(\frac{10^5}{3}-\frac{1}{3}\right)^2\)
