Let f be the function given by f(x)=2x/sqrt(x^2+x+1)

a)Find the domain for f. Justify your answer.

b)Write an equation for each horizontal asymptote of the graph f.

c)Find the range of f. Use f'(x) to justify your answer.

Note: f'(x)=(x+2)/(x^2 +x+1)^.5

Please help me with this problem. I don't really know how to do much of it.