Đáp án:
\(\begin{array}{l}
f)\forall x\\
g)\forall x\\
h)\forall x\\
i)x \in \emptyset \\
j)x \in \emptyset
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
f)DK:{x^2} + 1 \ge 0\left( {ld} \right)\forall x\\
KL:\forall x\\
g)DK:{x^2} + 2x + 3 \ge 0\\
\to {x^2} + 2x + 1 + 2 \ge 0\\
\to {\left( {x + 1} \right)^2} + 2 \ge 0\left( {ld} \right)\forall x\\
KL:\forall x\\
h)DK:{x^2} - 4x + 4 \ge 0\\
\to {\left( {x - 2} \right)^2} \ge 0\left( {ld} \right)\forall x\\
KL:\forall x\\
i)DK: - {x^2} - 3 \ge 0\\
\to {x^2} + 3 \le 0\left( {KTM} \right)\\
Do:{x^2} + 3 > 0\forall x\\
KL:x \in \emptyset \\
j)DK:{x^2} + 3 < 0\left( {KTM} \right)\\
Do:{x^2} + 3 > 0\forall x\\
KL:x \in \emptyset
\end{array}\)
