Помогите . алгебраические дроби

1.
$\frac{3a-9}{b+2}* \frac{3b+6}{18a-54}= \frac{3(a-3)}{b+2}* \frac{3(b+2)}{18(a-3)}= \frac{1}{2} \\ \\ \frac{ (a-2)^{2} }{b+5} : \frac{3a-6}{2b+10}= \frac{(a-2)(a-2)}{b+5}* \frac{2(b+5)}{3(a-2)}= \frac{2(a-2)}{3} \\ \\ \frac{2x}{5x-10}- \frac{x}{x-2}= \frac{2x}{5(x-2)} - \frac{x}{x-2}= \frac{2x-5x}{5(x-2)} =- \frac{3x}{5x-10}$

2.
$\frac{15b}{5-b} + \frac{6b}{b^{2} -25} * \frac{7b+35}{3}= \frac{15b}{5-b} + \frac{6b}{(b-5)(b+5)}* \frac{7(b+5)}{3}= \frac{15b}{5-b}+ \frac{14b}{b-5}= \\ \frac{15b}{5-b}- \frac{14b}{5-b} = \frac{b}{5-b}$

3.
$\frac{4}{ x^{2} +4x+4}:( \frac{ x^{2} +12}{ x^{2} -4} - \frac{x+2}{x-2})= \frac{4}{(x+2)(x+2)}:( \frac{ x^{2} +12}{(x-2)(x+2)}- \frac{x+2}{x-2})= \\ \frac{4}{(x+2)(x+2)}:( \frac{ x^{2} +12-(x+2)(x+2)}{(x-2)(x+2)})= \frac{4}{(x+2)(x+2)} * \frac{(x-2)(x+2)}{8-4x}= \\ \frac{4}{4(2-x)}= \frac{1}{2-x}$

при х=1
1/(2-1)=1/1=1