y′(x)=x+y/z z′(x)=x−y/y

Haiden Meyer

Haiden Meyer

Answered question

2022-09-28

I have a system of differential equations which I need to solve and obtain y(x) and z(x). I tried elimination method and got to a point but I don't know what to do after here. Any help would be appreciated Question:
y ( x ) = x + y z
z ( x ) = x y y

Answer & Explanation

Bestvinajw

Bestvinajw

Beginner2022-09-29Added 15 answers

y ( x ) = x + y z z ( x ) = x y y
y ( x ) z = x + y z ( x ) y = x y
Sum both differential equations:
y z + z y = 2 x
( y z ) = 2 x
y z = x 2 + C
The second DE is:
z ( x ) y = x y
z = x y 1
z = z x x 2 + C 1
That you can solve.

Some details
z = z x x 2 + C 1
You can't integrate both sides the way you did because there is the z function on RHS:
z z x x 2 + C = 1
x 2 + C z z x x 2 + C = x 2 + C
( z x 2 + C ) = 1 x 2 + C
Now you can integrate both sides.
z x 2 + C = d x x 2 + C + C 2
z ( x ) = x 2 + C ( C 2 arctan x x 2 + C )

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