I am new to dealing with 3D, and even simple stuff makes my head spin around. Sorry for the newbie question.

Lets say I have 2 vectors:

```
a(2,5,1)
b(1,-1,3)
```

These vectors "generate" a plane. How can I get a third vector perpendicular to both **a** and **b**?

I can do this in 2D using a vector c(A,B) and turning it into c'(-B,A).

Thanks for the help.