\( \frac{a+b}{a^{2}+b^{2}+2 a b}-a b \quad \) per \( a=4 ; b=-3 \)

1. \( \frac{4 x+5}{13}=\frac{8}{9} \)

\( \log _{3}(2 x-5)=-2 \) Simplify your ansh

42. \( \frac{3 x+y}{2 x+3+z} \quad \operatorname{per} x=-\frac{1}{9} \quad y=\frac{1}{2} \quad, \quad z=\frac{2}{9} \)

Simplificar y obtener la minima expresión: \( \frac{\frac{b}{a}+\frac{a-2 b}{b}}{\left(\frac{a^{2}+3 a b+3 b^{2}}{b}+\frac{b^{2}}{a}\right) \cdot(a-b)^{2}} \)

b) \( 5^{0}+\frac{1}{3} \cdot\left[\left(3-\frac{1}{5}\right) \cdot 5^{-2}+2 \cdot\left(1-\frac{2}{5}\right)^{3}\right]: \frac{4}{3} \)