TITLE: Differentiation, using d or delta
QUESTION [34 upvotes]: Are the symbols $d$ and $\delta$ equivalent in expressions like $dy/dx$? Or do they mean something different?
Thanks

REPLY [8 votes]: Here's the dummy version:
∂ is used when a function; say f(x,y,z) depends on more than 1 variable.
d is used when a function; say f(t) depends on only 1 variable.
Example:
You have f(x,y)   and  x(t)    and  y(t) 
In the end f only depends on t here, but in the chain it can depend on x or y, so you write:
df/dt = ∂f/∂x * dx/dt + ∂f/∂y * dy/dt     
You use df/dt, dx/dt and dy/dt here because they only depend on t. You use ∂f/∂x and ∂f/∂y because for f in this partial differential step f can go via both x or y. 
I hope this helps.
Good Luck