Bài 1:
\(a,A=\dfrac{x-5+2x+10-2x-10}{\left(x-5\right)\left(x+5\right)}=\dfrac{x-5}{\left(x-5\right)\left(x+5\right)}=\dfrac{1}{x+5}\\ b,A=\dfrac{1}{2}\Leftrightarrow x+5=2\Leftrightarrow x=-3\left(tm\right)\\ c,A\in Z\Leftrightarrow x+5\inƯ\left(1\right)=\left\{-1;1\right\}\\ \Leftrightarrow x\in\left\{-6;-4\right\}\left(tm\right)\)