Ответ:

1)

[tex] \frac{12my {}^{6} }{18m {}^{7} y {}^{2} } = \frac{2y {}^{4} }{3m {}^{6} } [/tex]

2)

[tex]16a + \frac{20b}{4ab} = 16a + \frac{5}{a} = \\ = 16a {}^{2} + 5[/tex]

3)

[tex]x {}^{2} - 10x + \frac{25}{x {}^{2} } - 25 = \\ = x {}^{4 } - 10x {}^{3} - 25x {}^{2} + 25[/tex]