What can be the solution at this link?

Questions
1

[DSolve::litarg—Wolfram Documentation

I](DSolve::litarg—Wolfram Documentation)n this link, For the second example, Why the solution was not given?

Is there no solution for it?

2

It’s an example of an error in specifying the problem. You need to change f[0,2t] to f[0,t]

3

Ok thank you.