a: Thay x=1/2 vào Q, ta được:
\(Q=\left(\dfrac{1}{4}-16\right):\left(\dfrac{1}{2}-3\right)=\dfrac{63}{10}\)
b: \(P=\dfrac{8}{x\left(x+4\right)}+\dfrac{5}{x+4}-\dfrac{2}{x}\)
\(=\dfrac{8+5x-2x-8}{x\left(x+4\right)}=\dfrac{3x}{x\left(x+4\right)}=\dfrac{3}{x+4}\)