The orthogonal trajectory for the family of curves ex+e−y=k is
We have, ex+e−y=k ....(1)
Differentiating w.r.t. x, we get
ex−e−ydydx=0 ....(2)
Replacing dydx with −dxdy in (2), we get
ex+e−ydxdy=0⟹eydy=−e−xdx
On integrating, we get
ey=e−x+c or ey−e−x=c