The domain of a function is the set of all allowable x values. What are the allowable values of x in the equation f(x)=sqrt(4-x)? Keep in mind that, in general, we don't allow values inside a square root sign to be negative. So our allowable values of x are:
4-x>=0=> x<=4
The range of a function is the set of y values associated with the domain. What are the resulting values of y? We know that, with x=4, y=0 and that is the lowest value of y we'll have. As x increases, y will increase also, albeit far more slowly. And so our range is:
y>=0
