Solve the first order hyperbolic equation

[hunt_mat]

Plug it in and see what sign causes you trouble (I think it'll be the - sign that will be the troublesome one). Look for large values of x to find the right sign. Then you're done, you've got the right solution!

 

[andrey21]

Which equation shall I plug the r value into?

Is it:

log u = x²/3 + log (2r+4) - r²/3

 

[hunt_mat]

Yes.