Question

помогите даю 20балов...
$( frac{a - 1}{a + 1} - frac{a + 1}{a - 1} ) div frac{2a}{1 - {a}^{2} } =$
$( frac{ {b}^{3} }{ {b}^{2} - 8b + 16 } - frac{ {b}^{2} }{b - 4} ) div ( frac{ {b}^{2} }{8 - 16} - frac{b}{b - 4} ) =$