1.

Solve ut + xux = 0 with the initial condition u(x, 0) = e−x2 .

Answer»

The equation for the characteristic curves are dt/1 = dx/x . 

Thus the characteristic curves are given by 

t = ln x + c', or 

xe−t = c. 

Therefore, the general solution of the equation is 

u(x, t) = f(xe−t). 

To determine f, we set t = 0 and find that 

f(x) = e−x2

Thus u(x, t) = e−x2e−2t



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