How do I find out if this equation is a function or not?

Question

The question is 

Determine if each relation is or is not a function.

And the questions are

1. y=2x²-3x+1

2. y=3/2x-4

3. y=-3x⁴+x³-2x+1

I would like to know the explainations. From the content of the workbook, I am guessing that somehow I need to find out if there are more than one domain using those equations.

If you know how to do these problems and can help, it would be great!

Thank you!

Answer 1

The simple answer (but not very explanatory answer) is that all polynomials are continuous functions on the whole real line.

Another answer which may make more sense is to graph each one of these and make sure that each graph does not cross any value of x more than once.