### Author Topic: section 2.1  (Read 1873 times)

#### Arush Mitra

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##### section 2.1
« on: September 21, 2016, 01:59:17 PM »
could someone please explain how do we get from equation 1 to equation 2. please check the attached file to view the equations.

#### Victor Ivrii

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##### Re: section 2.1
« Reply #1 on: September 21, 2016, 04:55:42 PM »
No, we do not get equation (2) from (1) but we observe that if (1) holds and we take $dx$, $dt$ satisfying (1) then

du=u_tdt +u_xdx= (u_t a + u_xb)\frac{dt}{a}=0.