Understanding d and Δ in Integration

[cheez]

How come d becomes (delta)? after integration? I thought d and delta is the same thing. What's the difference between them?

For example,
dA = - PdV

After intergration, it becomes
(delta)A = -(integral)PdV

I can't type the symbols.

thx!

 

[Dick]

If the integration is going say, from x0 to x1, then (delta)A is an abbreviation for A(x1)-A(x0). (integral)dA=A but applying the limits I get (delta)A. Not at all the same thing as the dA symbol.

 

[turdferguson]

Delta just means "change in" and is used for just plain change or average change, nothing instantaneous or infintesimal. With calculus, most of the deltas turn into d's, but not all as shown here