На 4 сделайте срочно.50 балов

$1.( \frac{x+5y}{ x^{2} -5xy} - \frac{x-5y}{ x^{2} +5xy} ) * \frac{25y^{2}- x^{2} }{5y^{2} } = (\frac{(x+5y)^{2}-(x-5y)^{2} }{x(x-5y)(x+5y)}) * \frac{(5y-x)(5y+x)}{5y^{2} } }$ = $\frac{(x+5y-x+5y)(x+5y+x-5y)}{-x(5y-x)} * \frac{5y-x}{5y^{2} } = \frac{10y*2x}{-x} * \frac{1}{5 y^{2} } = \frac{4x}{-5xy^{2} } =- \frac{4}{5 y^{2} }$
2. $(a+1+ \frac{1}{a-1} ): \frac{ a^{2} }{1-2a+ a^{2} } = \frac{ a^{2}-a+a-1+1 }{a-1} * \frac{(a-1)^{2} }{ a^{2} } = a^{2} * \frac{a-1}{ a^{2} } =a-1$
3. $( \frac{3}{(2-x)^{2} } + \frac{2}{ x^{2} -4} )*(x-2) ^{2} - \frac{5x}{x+2} =( \frac{2(x+2)}{(x-2) ^{2}(x+2) } + \frac{2(x-2)}{(x-2) ^{2}(x+2) } )$ * $(x-2) ^{2} - \frac{5x}{x+2} = \frac{2x+4+2x-4}{x+2} - \frac{5x}{x+2} = \frac{4x-5x}{x+2} =- \frac{x}{x+2}$
4. $\frac{1- \frac{3}{c} }{ \frac{6c-9}{c} -c} = \frac{ \frac{c-3}{c} }{ \frac{6c-9- c^{2} }{c} } =(c-3)*(6c-9- c^{2} )=(c-3)*6(c-3)- c^{2} =$ $6(c-3)^{2} -c^{2} =(6c-18-c)(6c-18+c)=(5c-18)(7c-18)$

** 4 сделайте срочно.50 балов