Answer
The graphs that represent y as a function of x are (a) and (d)
Work Step by Step
In the first graph:
The graph is parallel to the $x$ -axis and the equation of the graph is $y=c$ , where $c$ is a constant.
In the second graph:
The given graph is of the form $x=c$ , which is not a function of y.
In the third graph:
It represents a semicircle. If we draw a vertical line, it would intersect the said graph at two points, which is against the definition of a function. Hence, the graph is not a function of y.
In the fourth graph:
The fourth graph also represents a semicircle. Drawing a vertical line, it intersects the graph at only one point, satisfying the condition for being a function. Thus, the graph is the function of $y\left( x \right)$.
Hence, the graphs (a) and (d) represent y as functions of x.
