[Blindmath] D Y verses Delta Y

[GianniP46]

Hi all,
I am brushing up on some Calculus.  I find myself confused between the difference d y and delta y and d x and delta x.  It seams that d x and delta x are usually the same, but there is a difference between d y and delta y.
For example, if you have a function Y = X squared, and you want to find d y and delta y at x = 2 and d x =1,
Then
D Y = 2X DX which = 2 times2 times 1 which =4
Delta y = f of x plus delta x minus f of x
which = (x + delta x) squared minus x squared
which = (2+1) squared minus 2 squared
which = 9  minus 4 = 5
so d x = 4 and d y = 5.

I understand that d y is the y component or the rise of the slope of the tangent line at x = 2 of x squared, but what does a delta y value of 5 mean for this function?

The book I am looking at makes it seam that d y has to do with the y component of the tangent line and delta y has to do with the y component of the curve.  This is not making sense to me for some reason.  Can someone explain?  Feeling very dumb and frustrated right now. lol


Gian Carlo Pedulla
GianniP46 at earthlink.net

LETS! GO! METS!