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473
$\frac{b}{a - b} \times ( \frac{1}{a} - \frac{1}{b} ) = ( \frac{b}{ab} - \frac{a}{ab} ) = \frac{b - a}{ab}$
$\frac{b}{a - b} \times - \frac{(a - b)}{ab} = - \frac{1}{a}$
474
$\frac{b}{2a - b} \times ( \frac{1}{a} - \frac{2}{b} ) = \frac{b}{2a - b} \times( \frac{b}{ab} - \frac{2a}{ab} ) = \frac{b}{2a - b} \times - \frac{(2a - b)}{ab } = - \frac{1}{a}$
475
$\frac{a}{a - 3b} \times ( \frac{3b}{ab} - \frac{a}{ ab} ) = \frac{a}{a - 3b} \times - \frac{(a - 3b)}{ab} = - \frac{1}{b}$
476
$\frac{a}{5a - 7b} \times ( \frac{7b}{ab} - \frac{5a}{ab} ) = \frac{a}{5a - 7b} \times - \frac{(5a - 7b)}{ab} = - \frac{1}{b}$
477
$( \frac{u}{ v} + \frac{4v}{u} - 4) \times \frac{uv}{2v - u} = (\frac{ {u}^{2} + 4 {v}^{2} - 4uv }{vu} ) \times \frac{uv}{2v - u} = \frac{ {(2v - u)}^{2} }{vu} \times \frac{uv}{2v - u} = 2v - u$