What is the range of f(x)=4x2+1f(x) = \frac{4}{x^2 + 1}f(x)=x2+14?
(0,4](0, 4](0,4]
[0,4)[0, 4)[0,4)
[1,4][1, 4][1,4]
(0,∞)(0, \infty)(0,∞)