General Solution for the characteristics of 2 quasi linear PDE's
I am stuck on how the general solutions where obtained for the following quasi linear PDE's. I understand this to be quasi linear because the highest derivative of u is linear even though e^u is nonlinear.
1) and 2)
I calculate the characteristics of 1) and 2) as
hence however I dont know how this arrived at
How are there 2 constants a and b when it is only a first order ODE?
hence which arrives at
I dont know how x,y and t+c are determined?
Any tips will be appreciated.