Every time I try to use the solve function in Mathematica 10 for Students, I get the error "0 is not a valid variable". Here's what I've been entering:
Solve[2x^3 + x^2 + 2 == 0, x]
I also tried to enter an example of the solve function from the Mathematica documentation, and that also did not work.
John is right, thank you very much. I fixed it.
Usually, this kind of error is the result of having set x=0 earlier in the session.
Strange, it works in Mathematica 10 Home Edition. Are you sure you typed it in as you've shown?