# Using Computations, How do you determine if a vector field is radial?

I have looked at the graph. As far as I know, radial is when all of the vectors are pointing away from the orgin, which they are. How can I prove if a function is radial (not just look at a graph). I would like a formula, not an example. Even if my function is not radial, I would still like to know computations to prove if a vector field is radial or not.

My function F(x-y, y+x) For a graphing site: http://kevinmehall.net/p/equationexplorer/vectorfield

Function: (x-y)i+(x+y)j

Thank you!

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A field $\vec F(\vec r)$ is radial if for every position vector $\vec r$ the vectors $\vec F(\vec r)$ and $\vec r$ are collinear. That is, one is a scalar multiple of the other.