Wednesday, 26 November 2014

Why is it legitimate to solve the differential equation fracdydx=fracyx by taking intfrac1ydy=intfrac1xdx?




Answers to this question Homogeneous differential equation dydx=yx solution? assert that to find a solution to the differential equation dydx=yx we may rearrange and integrate 1y dy=1x dx. If we perform the integration we get logy=logx+c or y=kx for constants c,kR. I've seen others use methods like this before too, but I'm unsure why it works.



Question: Why is it legitimate to solve the differential equation in this way?


Answer



You start with
y=yxyy=1xydxy=dxx,
and you make the change of variables in the first integral, which results in what you've written

dyy=dxx


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...