a) `ĐK : x^2+3 ≥ 0 \forall x \in mathbbR`
b) `25-4x^2 ≥ 0 <=> -5/2 ≤ x ≤ 5/2`
c) `2x^2-5x+3 ≥ 0 <=> x ≤ 1; 3/2 ≤ x`
d) `2x-x^2 > 0 <=>0 < x<2`
e) `x^2-5x+6>0<=>x<2;3<x`
f) $\begin{cases}x-3>0\\5-x>0\\\end{cases}$
`<=>` $\begin{cases}x>3\\x<5\\\end{cases}$
`<=> 3<x<5`