The domain of the function $f(x)=\frac{x^2+1}{x^2-3 x+2}$ is

$R-\{-1,1\}$ $R$ $R-\{1,2\}$ $R-\{3,-2\}$

$R-\{1,2\}$

The correct answer is Option (3) → $R-\{1,2\}$