Answer
It is a function.
Domain = $[-\frac{1}{4}, \infty)$
Range = $[0, \infty)$
Work Step by Step
Refer to the curve $y = \sqrt{4x + 1}$ in Graph I, it is a function because
by way of Vertical Line Test, each vertical line drawn will not intersect the curve on the graph in more than one point, so, the equation defines a function.
For $y = \sqrt{4x + 1}$, one corresponding value of y can always be found for any choice of x in the domain of $[-\frac{1}{4}, \infty)$.
y will be any real number with range $[0, \infty)$.
