\(A=\frac{4^{20}-2^{20}+6^{20}}{6^{20}-3^{20}+9^{20}}\)
\(A=\frac{2^{20}.2^{20}-2^{20}+3^{20}.2^{20}}{2^{20}.3^{20}-3^{20}+3^{20}.3^{20}}\)
\(A=\frac{\left(2^{20}-1+3^{20}\right).2^{20}}{\left(2^{20}-1+3^{20}\right).3^{20}}\)
\(\Rightarrow A=\frac{2^{20}}{3^{20}}\)