/sci/ - Science & Math

"Which of these relations A -> R, A= [-1; 2] , represents a function?"
Answer key says a & d.
Now, it's quite obvious to me that b) is not a function since it doesn't pass the vertical line test, but
why is d) considered a function if the graph extends a bit further from the domain? And
why is c) not a function?

"Which of these relations A -> R, A= [-1; 2] , represents a function?"
Answer key says a & d.
Now, it's quite obvious to me that b) is not a function since it doesn't pass the vertical line test, but
why is d) considered a function if the graph extends a bit further from the domain? And
why is c) not a function?