After I read section 2.6 of online textbook, I find out there are two places need professor to clarify.

1. After equation (7), you have written

"Therefore, Ï•(x+ct) and Ïˆ(xâˆ’ct) are defined respectively as x+ct>0 (which is automatic as x>0,t>0) and xâˆ’ct<0 (which is fulfilled only as x>ct)." -- Indeed (PS. Don't use red--I use it)

Should the equation with read color be xâˆ’ct>0?

2. Picture "Fig-2.6.2" cannot be displayed. After I checked code of the website, it displayed 404 ERROR (page not found).

Without this picture, I cannot quite understand context in " 1D Wave equation on the finite interval ".

Was wrong address for an image. Fixed

Thanks for your assistance.