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**Home Assignment 2 / Re: Concept: Where does the (-) come from **

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**Today**at 04:49:49 PM »

Do you mean $u_t + tu_x=0$? Then $\frac{dt}{1} = \frac{dx}{t}=\frac{du}{0}$. The first equation implies $$dx=tdt \implies x=\frac{1}{2}t^2+C\implies x-\frac{1}{2}t^2=C.$$