\(a,ĐK:x\ne1;x\ne\pm3\\ A=\dfrac{x^2-1+x^2-9}{\left(x-3\right)\left(x-1\right)}-\dfrac{14+2x^2}{\left(x-1\right)\left(x+3\right)}\\ A=\dfrac{\left(2x^2-10\right)\left(x+3\right)-\left(2x^2+14\right)\left(x-3\right)}{\left(x-1\right)\left(x-3\right)\left(x+3\right)}\\ A=\dfrac{2x^3+6x^2-10x-30-2x^3+6x^2-14x+42}{\left(x-1\right)\left(x-3\right)\left(x+3\right)}\\ A=\dfrac{12x^2-24x+12}{\left(x-1\right)\left(x-3\right)\left(x+3\right)}\\ A=\dfrac{12\left(x-1\right)^2}{\left(x-1\right)\left(x-3\right)\left(x+3\right)}=\dfrac{12\left(x-1\right)}{\left(x-3\right)\left(x+3\right)}\\ b,\left|x+4\right|=5\Leftrightarrow\left[{}\begin{matrix}x=5-4=1\left(ktm\right)\\x=-5-4=-9\end{matrix}\right.\\ \Leftrightarrow A=\dfrac{12\left(-10\right)}{\left(-12\right)\left(-6\right)}=-\dfrac{5}{3}\)
