I do not understand the concept of differential enter image description here for example
What have both the sides been differentiated by to get this result.I understand that dz^2/dz gives 2z,where has the extra dz come from also what has the side with theta been differentiated by to get this result,it cannot be dz.If its dtheta how can you differentiate something with respect to another thing in two sides of an equation.Can someone explain this and how did dz and dtheta come in the equations.