Solve n(xy-2/y^2)^21

$$n ( x y - \frac { 2 } { y ^ { 2 } } ) ^ { 21 }$$

Evaluate

$$\frac{n\left(xy^{3}-2\right)^{21}}{y^{42}}$$

Expand

$$n\left(xy\right)^{21}-42ny^{18}x^{20}+840ny^{15}x^{19}-10640ny^{12}x^{18}+95760ny^{9}x^{17}-651168ny^{6}x^{16}+3472896ny^{3}x^{15}-14883840nx^{14}+\frac{52093440nx^{13}}{y^{3}}-\frac{150492160nx^{12}}{y^{6}}+\frac{361181184nx^{11}}{y^{9}}-\frac{722362368nx^{10}}{y^{12}}+\frac{1203937280nx^{9}}{y^{15}}-\frac{1666990080nx^{8}}{y^{18}}+\frac{1905131520nx^{7}}{y^{21}}-\frac{1778122752nx^{6}}{y^{24}}+\frac{1333592064nx^{5}}{y^{27}}-\frac{784465920nx^{4}}{y^{30}}+\frac{348651520nx^{3}}{y^{33}}-\frac{110100480nx^{2}}{y^{36}}+\frac{22020096nx}{y^{39}}-\frac{2097152n}{y^{42}}$$