For n ≥ 1. Suppose u ∈ C^2(Rn ×[0,∞)) solves the heat equation u_t − ∆u = 0. Let u(x, t) = v((|x|^2)/t). Show that v satisfies 4*z*v′′(z) + (2n + z)*v′(z) = 0, where z = (|x|^2)/t. And find the general solution of the equation for v.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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For n 1. Suppose u ∈ C^2(Rn ×[0,∞)) solves the heat equation u_t − ∆u = 0. Let u(x, t) = v((|x|^2)/t). Show that v satisfies 4*z*v′′(z) + (2n + z)*v′(z) = 0, where z = (|x|^2)/t. And find the general solution of the equation for v.

Expert Solution
Step 1: Conceptual Introduction

The heat equation utΔu=0 is a partial differential equation (PDE) that describes how a distribution of heat evolves over time.

In n dimensions, the Laplacian operator Δ is defined as Δu=i=1n2uxi2.

The function u(x,t) is assumed to be twice continuously differentiable.

The problem at hand is to show that if u(x,t)=v(|x|2t) , then v satisfies a certain ordinary differential equation (ODE), and to find the general solution of that ODE.

Here z=|x|2t and |x|2=x12+x22++xn2 .


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