# Analytical solution

## Main Question or Discussion Point

hallo I ams earching analytical solution for system of two ODE in next form

x*(dy/dr) - (y*y/r) = constant1*r*r*x*x*x
x*(dy/dr)+(x*y/r)=constant2*r*r*x*x*(r*constant3-y)

where x(r) and y(r). conditions are x=constant4 at r=constant5 and y=0 at r=constant5

thnx

r.

## Answers and Replies

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HallsofIvy
Homework Helper
(r^2x^3 is simpler than r*r*x*x*x)

Do both equations have "dy/dr"? If neither equation involves dx/dr, you can treat x as a constant. In fact, if we write the two equations as x(dy/dr)= y^2/r+ C1r^2x^3 and x(dy/dr)= -xy/r+ C2r^2x^2(C3- y) and, because the two left sides are equal, equate the two right sides: y^2/r+ C1r^2x^3= -xy/r+ C2r^2x^2(C3- y). You can solve that for y as a function of both x and r and then put that back into the equation to get a single equation for y.

hallo like this:
x*(dy/dr) - (y*y/r) = constant1*r*r*x*x*x
x*(dx/dr)+(x*y/r)=constant2*r*r*x*x*(r*constant3-y)

where x(r) and y(r). conditions are x=constant4 at r=constant5 and y=0 at r=constant5