Question

??????????????????????????????

Answer 1

$\frac{5b}{b-3} -\frac{b+6}{2b-6} *\frac{90}{b^2+6b} =\frac{5b}{b-3} -\frac{b+6}{2(b-3)} *\frac{90}{b(b+6)}==\frac{5b}{b-3} -\frac{45}{b(b-3)} =\frac{5b^2-45}{b(b-3)}=\frac{5(b^2-9)}{b(b-3)}=\frac{5(b-3)(b+3)}{b(b-3)}=\frac{5(b+3)}{b}$$(\frac{a-b}{a+b} -\frac{a+b}{a-b} ):\frac{16a}{64-a^2} =\frac{(a-b)^2-(a+b)^2}{a^2-b^2} *\frac{64-a^2}{16a} =\frac{a^2-2ab+b^2-a^2-2ab-b^2}{a^2-b^2} *\frac{64-a^2}{16a} =\frac{-4ab(64-a^2)}{16a(a^2-b^2)} =\frac{-b(64-a^2)}{4*(a^2-b^2)} =\frac{b(a^2-64)}{4*(a^2-b^2)} =\frac{b(a-8)(a+8)}{4*(a-b)(a+b)}$