Find the number of unique solutions of the

Jefferson Pacheco

Jefferson Pacheco

Answered question

2022-04-13

Find the number of unique solutions of the following nonlinear ODE
y=103xy25,y(0)=1

Answer & Explanation

entreblogsmc2j

entreblogsmc2j

Beginner2022-04-14Added 10 answers

Step 1
Let z=y15,
hence
y (x)=(z5) (x)=103xz(x)2=(5z4z)(x)=20z3(x)z(x)2+5z(x)4z (x),
which is equivalent to
5z(x)2[z(x)2z (x)+4z(x)3z(x)223x]=0,
implying z(x)=0 or
z(x)2z (x)+4z(x)3z(x)223x=0.
I do not believe this latter equation can be solved analytically.
Step 2
Given the way you phrased the problem, and given how you went about mistakenly solving it, I assume you actually meant to write the differential equation as
y'(x)=103xy(x)25,

instead. Then having only one boundary condition is justified in this situation. This can be solved with separation of variables. Hence
y(x)=0 or
y(x)-25y'(x)=103x53y35'(x)
=(53x2)'y35'(x)=(x2)'.
By Riemann integrating, you obtain
y(t)35-y(0)35=t2.Z
So in fact, you do obtain y(t)=(t2-1)53, and this is the only solution everywhere in R

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