Ответ:

[tex]4) {a}^{4} \times ( \frac{3a + b}{a} - 3 {)}^{2} + {b}^{4} \times {( \frac{a - 2b}{b} + 2) }^{2} - 2 {(ab)}^{2} = {a}^{4} \times {( \frac{ 3a + b - 3a}{a} )}^{2} + {b}^{4} \times {( \frac{a - 2b + 2b}{b} )}^{2} - 2 {a}^{2} {b}^{2} = {a}^{4} \times \frac{ {b}^{2} }{ {a}^{2} } + {b}^{4} \times \frac{ {a}^{2} }{ {b}^{2} } - 2 {a}^{2} {b}^{2} = {a}^{2} {b}^{2} + {a}^{2} {b}^{2} - 2 {a}^{2} {b}^{2} = 0[/tex]

[tex]5)3 + ( \frac{28c}{ {c}^{2} - 49 } + \frac{c - 7}{c + 7} ) \times \frac{c}{c + 7} - \frac{c}{c - 7} = 3 + \frac{28c + {c}^{2} - 14c + 49}{(c - 7)(c + 7)} \times \frac{c}{c + 7} - \frac{c}{c - 7} = 3 + \frac{ (c + 7) {}^{2} }{(c - 7)(c + 7)} \times \frac{c}{c + 7} - \frac{c}{c - 7} = 3 + \frac{c}{c - 7} - \frac{c}{c - 7} = 3 [/tex]

[tex]6)4.5 + \frac{25 {x}^{2} - {4}^{ - 1} }{5x + {2}^{ - 1} } - 3x = 4.5 + \frac{25 {x}^{2} - \frac{1}{4} }{5x + \frac{1}{2} } - 3x = 4.5 + \frac{(5x - \frac{1}{2})(5x + \frac{1}{2}) }{5x + \frac{1}{2} } - 3x = 4.5 + 5x - \frac{1}{2} - 3x = 4 + 2x = 2(2 + x)[/tex]