## Nullclines

I have a simple question regarding nullclines, as I'm having trouble determining the correct direction errors.

For example, here's a system of equations:

dx/dt = 2-x-y

dy/dt=y-x^2

x-null is y= -x + 2
y-null is y= x^2

x-null is vertical, y-null goes horizontal.

But when I divide the graph in different sections, and pick different plot points which equations do I plug into to find directions?

I know that wasn't clear, but for example:

If I want to know if on the y-null if the direction of a certain section is pointing left or right, would I plug the points I chose in:

A) dy/dt = y-X^2
B) dx/dt=2-x-y

or C) y=x^2

I'm not sure which equation to plug it in. I've tried to think it out, but I end up always confusing myself. Please point me in the right direction. Thanks.
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