Question 898961
{{{f(x)= sqrt( x^4-16x^2)}}}
{{{f(x)=sqrt((x^2)(x^2-16))}}}
{{{f(x)=x*sqrt(x^2-16)}}}
Your work appears on the right track.


{{{x^2-16>=0}}}
{{{(x-4)(x+4)>=0}}}


Critical values for the domain are 4 and -4.  Three intervals of the x-axis
can be checked.
You will find the domain is the UNION of {{{highlight(x<-4)}}} and {{{highlight(x>4)}}}.