Номер 12,найдите пожалуйста область определения функции и 13 решить систему уравнений

{x²-1≥0
{16-x²>0
(x-1)(x+1)≥0
x=1 x=-1
x≤-1 U x≥1
(4-x)(4+x)>0
x=4 x=-4
-4 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
--------(-4)------------[-1]----------------[1]---------------(4)-------
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
x∈(-4;-1] U [1;4)