> Maths: Solve xdy/dx=y+xy?

Maths: Solve xdy/dx=y+xy?

Posted at: 2015-01-07 
Please Help!

xdy/dx=y+xy





x dy/dx = y(x+1)



x dy = y(x+1) dx





separate the variables



dy/y = (x+1)/x dx



dy/y = (1+1/x) dx





Integrate both sides



ln y = x + ln x +c1



y = e^(x+ln x+c1)





y = e^x e^ln x e^c1



let e^c1 = C





y = C x e^x

Divide both sides by xy:





1/y * dy/dx = 1/x + 1





1/y * dy = (1/x + 1)dx





Integrate both sides:





ln|y| = ln|x| + x + C





Now make y the subject, raise both sides to the base of e:





|y| = e^[ln|x| + x + C]





Simplifying:





|y| = e^ln|x| * e^(x) * e^C





As C is just a constant, e^C is also a constant so we can replace e^C with C:





y = Ce^(x)

I am not sure if you worded the question correctly but if this is what you meant I'll answer this:





F(x) = y+xy now dy/dx of F(x) = x+1

x(dy/dx) = y(1 + x)





dy/y = (1 + x)/x dx





Integrating both sides:





ln|y| = ln|x| + x + C





y = C*x*e^(x)

Please Help!