\(\dfrac{4^{61}-2^{121}}{8^{40}}=\dfrac{2^{122}-2^{121}}{2^{120}}=\dfrac{2^{120}\left(2^2-2\right)}{2^{120}}=2\)
\(\dfrac{4^{61}-2^{121}}{8^{40}}\)
\(=\dfrac{2^{122}-2^{121}}{8^{40}}\)
\(=\dfrac{2^{122}-2^{121}}{2^{120}}\)
\(=\dfrac{\left(2-1\right)2^{121}}{2^{120}}\)
\(=\dfrac{1.2^{121}}{2^{120}}\)
\(=1.2\)
\(=2\)