Starting Out with PDEs: Solving au_x + bu_y + cu = 0

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Homework Statement


Hey I'm trying to get a sense of this problem, just starting pde class:

au_x+bu_y+cu=0


Homework Equations





The Attempt at a Solution


Dunno what to do with that last term
 
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Have you tried separation of variables?
 
This equation can be solved via the method of characteristics.
 
what is the method of characteristics?
 
This is something which should be covered in your course or alternatively you can google it ot it should be in any good book on PDEs.
 
The idea is basically to view the solution of the PDE as a surface u=u(x,y) and the equation is in fact the dot product between the normal at that point and the tangent plane. You just integrate up the equations for the tangent plane basically.
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...
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