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Jun14-11, 05:43 AM
P: 2,568
Quote Quote by lavinia View Post

given a small change in x, dx, the change is x^2 is close to 2xdx and the change in y^2 is close to 2ydy. But dy = (dy/dx)dx.

If y were independent of x then dy/dx would be zero. This would just mean that x can change without a change in y. But the constraint C = x^2 + y^2 tells you that y is a function of x, at least locally.
If I were to graph all three of those "derivatives" what would they look like? How do yuo even graph Fx alone?