Prove that the system of differential equations x=y, y=1+x^2−(1−x)y doesn't contain periodic solutions.

Kayla Mcdowell

Kayla Mcdowell

Answered question

2022-10-29

Prove that the system of differential equations
x ˙ = y y ˙ = 1 + x 2 ( 1 x ) y
doesn't contain periodic solutions.

Answer & Explanation

aitorarjolia

aitorarjolia

Beginner2022-10-30Added 11 answers

For any solution, x is unbounded. Use x for x ˙ .
x = y = 1 + x 2 ( 1 x ) y = 1 + x 2 ( 1 x ) x x + ( 1 x ) x = 1 + x 2 1.
Integrating
x + x x 2 2 t + c 1  for some constant  c 1 .
Then
x + x t + c 1 + x 2 2 t + c 1 .
Multiplying by e t :
( e t x ) ( t + c 1 ) e t .
Integrate and obtain that x ( t ) grows at least as t 2 / 2 as t .

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