Question related to PDE y(z_x)+x(z_y)+z=y

[coverband]

To solve the PDE:
y(z_x)+x(z_y)+z=y

Use Method of characteristics
a=y
b=x
d-cz=y-z

Thus
dx/y=dy/b=dz/(y-z)

Taking first and second term
xdx=ydy
x^2-y^2=A
x=sqrt(y^2+A)

My question is, at this stage of the calculation, must we account for a negative constant A such that
x=sqrt(y^2-A)
and if not why not?

Thank you

 

[matematikawan]

To be honest I'm not familier with the method.

Is it not that your x and y are the independent variables? So what is the domain for the solution function. A is just a constant. It can be positive or negative. I think!

 

[coverband]

Anyone else!?