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## Homework Statement

Find the ODE of the following

(1) du/dy = -u

(2) d^2u/dxdy = -du/dx

## Homework Equations

For question 1, the answer is u= A(x)e^(-y)

while for question 2, the answer is u= e^(-y)(B(X) + c(Y))

## The Attempt at a Solution

I've already solved the question, but just want to ask, if i change (1) to (2), its just a differentiation with respect to dx, but yet the solution contain a c(Y) term, any idea why is this so?