I'm trying to find the roots of relatively simple polynomial expressions, programmatically.

I found solve(expr, var) returns a list of equations that satisfy expr and found that using args on this list elements will list [var, val_i] and was wondering if this is the most direct approach?

I tried allroots but I get an error "not a polynomial" for anything I tried plugging in, whether an expression or an equation (e.g. I tried var + 8; var+8 = 0; var^2 + 16 etc.).