If we had an equation of the form
$f(r)+g(\theta)+\theta^2+c+2r+k(\theta)+10=0$
Is there a way to move the terms containing $r$ to one side and the terms containing $\theta$ to other side like this
$f(r)+c+2r+10=-g(\theta)-\theta^2-k(\theta)$
Thanks.
One possible way (used $x$ for $\theta$ as easier to type)
ClearAll[f, r, g, x, c, k]; eq = f[r] + g[x] + x^2 + c + 2 r + k[x] + 10 == 0 
eq = eq /. (stuff_) == 0 :> stuff; eq = List @@ eq; lhs = Pick[eq, Not@FreeQ[#, r] & /@ eq]; rhs = Complement[eq, lhs]; eq = Plus @@ lhs == -(Plus @@ rhs) 
