Answer
The given equation $2x+y=8$ defines y as a function of x.
Work Step by Step
Let us consider the following equation: $2x+y=8$
Isolate y on the left in the above equation
$y=-2x+8$
The above equation will provide a unique value of y for different values of x.
Again, apply the vertical line test according to which if any vertical line (parallel to the x-axis) intersect a provided graph in two different points, then it is not a function.
Since the graph of the equation will be a straight line, thus no vertical line will intersect the graph in more than one point.
Thus, the equation defines y as a function of x.
