Finding Solution of Inhomogeneous Heat Equation

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Homework Statement



Show that if u(x,t) and v(x,t) are solutions to the Dirichlet problems for the Heat equation

u_t (x,t) - ku_xx (x,t) = f(x,t), u(x,0) = Φ₁(x), u(0,t) = u(1,t) = g₁(t)

v_t (x,t) - kv_xx (x,t) = f(x,t), v(x,0) = Φ₂(x), v(0,t) = v(1,t) = g₂(t)

and if Φ₂(x) ≤ Φ₁(x) for 0 ≤ x ≤ 1, g₂(t) ≤ g₁(t), t > 0, then for all 0 < x < 1, t >0, we have u(x,t) ≥ v(x,t)

Homework Equations





The Attempt at a Solution



Following steps of example 2 and 3 of the following link, but I don't really understand what they are doing

http://www.math.mcgill.ca/jakobson/courses/ma264/pde-heat.pdf
 
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There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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