select all of the following graphs which represent $y$ as a function of $x$.

select all of the following graphs which represent $y$ as a function of $x$.
Answer
Explanation:
Step1: Apply Vertical Line Test
A graph represents $y$ as a function of $x$ if no vertical line intersects the graph more than once.
Step2: Test Top Graph
Any vertical line intersects the horizontal line $y=1$ exactly once. So it is a function.
Step3: Test Middle Graph
Any vertical line intersects the diagonal line exactly once. So it is a function.
Step4: Test Bottom Graph
A vertical line (e.g., $x=-2$) intersects the ellipse twice. So it is not a function.
Answer:
The top horizontal graph and the middle diagonal graph represent $y$ as a function of $x$ (check the boxes next to these two graphs).