How do I find the domain if it is just x+7/3x

How do I find the domain if it is just x+7/3x

I really don't understand Domain and Range equations. And I need help solving this. Y = √2x - 2 Any help?

for the following function find the domain D and range T and show that for every c ∈ T there exists x,y such that f(x,y) = c. Sketch the Domain. The following is my own answer but I am unsure...

f(x)=2 sqr(-x^2+4) - 2 the range is R:{y| -2 ≤ y ≤ 2, yER) How do i get this answer?

I an trying to find the domain and range of f(x) square root x-3