4.
a) y=⁴√(3-x)
3-x≥0
-x≥ -3
x≤3
D(y)=(-∞; 3]
б) y=√(7-x)/(4-x²)
7-x ≥ 0
4-x²
ОДЗ: х≠2 и х≠ -2
(7-х)(4-х²)≥0
-(х-7)(-(х² -4))≥0
(х-7)(х²-4)≥0
(х-7)(х-2)(х+2)≥0
х=7 х=2 х= -2
- + - +
-------- -2 --------- 2 ----------- 7 ----------
\\\\\\\\\\ \\\\\\\\\\\\\\
х∈(-2; 2)U[7; +∞)
D(y)=(-2; 2)U[7; +∞)