Is this a function y=x-2? why or why not....the domain is {1 2 3 4} the co-domain= Z.....im so lost?

Question

Is this a function y=x-2? why or why not....the domain is {1 2 3 4} the co-domain= Z.....im so lost?

Answer 1

Relax :)

Yes, y = x - 2 is a function because every x-coordinate has a different y-coordinate.  You may have also learned about the vertical line test.  A graph IS a function if you can draw any vertical line and only hit the graph once, as is the case in y = x - 2.  

If the domain is 1,2,3,4, then some ordered pairs on the graph are :

x = 1  ===>  y = 1 - 2 ===>  y = - 1 .....so (1, - 1)

x = 2  ===>  y = 2 - 2 ===>  y =  .....so (2, 0)

x = 3  ===>  y = 3 - 2 ===>  y = 1 .....so (3, 1)

x = 4  ===>  y = 4 - 2 ===>  y = 2 .....so (4, 2)

every x goes to exactly one y-value, meaning that each x-coordinate only appears once :)

co-domain = Z (Which represents the sets of integers so x could be ...-3, -2, -1, 0 , 1, 2, 3, ...)

Good luck to you !