a: \(R=1:\dfrac{x^2+2+x^2-1-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(=1:\dfrac{x^2-x}{\left(x-1\right)\left(x^2+x+1\right)}=\dfrac{x^2+x+1}{x}\)
b: \(R-3=\dfrac{x^2+x+1-3x}{x}=\dfrac{\left(x-1\right)^2}{x}>0\)
=>R>3
c: Thay x=1/4 vào R, ta được:
\(R=\left(\dfrac{1}{16}+\dfrac{1}{4}+1\right):\dfrac{1}{4}=\dfrac{21}{4}\)