1.

Show that the differential equation `xcos(y/x)(dy)/(dx)=ycos(y/x)+x`is homogeneous and solve it.

Answer» Let `y/x = v`
Then, `y = vx =>dy/dx = v+x(dv)/dx`
So, given equation becomes,
`xcosv(dy/dx) = vxcosv+x`
`=>dy/dx = (vxcosv+x)/(xcosv)`
`=> v+x(dv)/dx = (vcosv+1)/(cosv)`
`=> v+x(dv)/dx = v+secv`
`=>x(dv)/dx = secv`
`=>cosdv = dx/x`
Integrating both sides,
`=> sinv = ln(x)+c`
`=>sin(y/x) = ln(x)+c`, which is the required equation.


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