Linearity of boundary conditions

[sarideli18]

Homework Statement

Using the definition of linearity to determine whether or not ech case is a linear homegeneous boundary condition:

i.) Uxx(0,y)=Ux(0,y)U(0,y)
ii.)Uy(x,0)=Ux(5,y)

Homework Equations

The Attempt at a Solution

I know Uxx(0,y)=Ux(0,y)U(0,y) is not linear because of U(0,y). However, I have no idea for ii.

 

[HallsofIvy]

Well, what does "linear" mean?