По формуле

[tex](a-b)^2=a^2-2ab+b^2[/tex]

[tex](\frac{9}{10}-\frac{1}{4}m^9)^2=(\frac{9}{10} )^2 -2\cdot \frac{9}{10}\cdot \frac{1}{4}m^9+(\frac{1}{4}m^9)^2=\frac{81}{100}-\frac{9}{20}\cdot m^9+\frac{1}{16}m^{18}= \frac{1}{16}m^{18} -\frac{9}{20}\cdot m^9+\frac{81}{100}[/tex]