a) TXĐ: \(D = \left\{ {x \in\mathbb R|x \ne 0,x + 1 \ne 0} \right\} \)\(=\mathbb R\backslash \left\{ {0; - 1} \right\}\)
b) TXĐ: \(D =\)\( \left\{ {x \in\mathbb R|{x^2} - 4 \ne 0,{x^2} - 4x + 3 \ne 0} \right\}\) \( =\mathbb R\backslash \left\{ { \pm 2;1;3} \right\}\)
c) TXĐ: \(D =\mathbb R\backslash {\rm{\{ }} - 1\} \)
d) TXĐ: \(D = \left\{ {x \in \mathbb R|x + 4 \ne 0,1 - x \ge 0} \right\} \) \(= ( - \infty ; - 4) \cup ( - 4;1]\)