Find the domain of the function algebraically q(r)=3square root r^2 -16

Hello : 
q(r)=3√(r²-16)
q  exist : r² - 16 ≥ 0
r² ≥ 16
√r² ≥ √16
but :  √16 = 4    and  √r² = |r |
|r | ≥ 4
r ≤ 4 or  r  ≥ 4 
the domain is :  ] -∞, 4] ∪  [,4 , + ∞ [ 

In this problem it decreased 20%