Помогите номер 13 второй и третий

1.
$.......= \frac{a+a+1}{a+1} * \frac{1+a}{2a+1}= \frac{2a+1}{a+1}* \frac{1+a}{2a+1}=1$

2.
..........= $( \frac{m}{n^{2}}- \frac{1}{m} ):( \frac{1}{n}+ \frac{1}{m})= \frac{m^{2}-n^{2} }{n ^{2}m } * \frac{nm}{m+n}= \frac{(m-n)(m+n)}{n^{2}m }* \frac{nm}{m+n}= \frac{m-n}{n}$

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