Хотя бы ответы. Даю14 балов

912. a)   ..........=[latex] \frac{x(x-4)}{x(x+7)} * \frac{(7-x)(7+x)}{6((4-x)} = \frac{-(7-x)}{6} = \frac{x-7}{6} \\ \\ b) .....= \frac{y(y^{2}-16) }{2(y+9)}* \frac{y(y+9)}{4-y}= \frac{ -y^{2} (4-y)(y+4)}{2(4-y)}= \frac{-y^{3}-4y }{2} [/latex] в)   ..........=b/4a г)   ..........=[latex] \frac{5(c-1)( c^{2}+c+1) }{c+2}* \frac{13(c+2)}{c^{2}+ c+1}=65(c- 1)[/latex]