`a) D = RR \\ {5}`
`PT`
`<=> 2x + 1 = 0`
`<=> x = -1/2`
`b) D = RR \\ {1}`
`PT`
`<=> x^2 - 4x + 3 = 0`
`<=> (x - 3)(x - 1) = 0`
`<=>` \(\left[ \begin{array}{l}x = 3\\x = 1\end{array} \right.\)
`=> x = 3`
`c) D = RR \\ {+-2}`
`PT`
`<=> x - 2 = 0`
`<=> x = 2` (loại)
`=> x in ∅`
`d) D = RR \\ {+-1}`
`PT`
`<=> 2x + 5 = 0`
`<=> x = -5/2`
