Math Exam 2 - Solutions to Heat Equation and Laplace's Equation Problems, Exams of Differential Equations

Download Math Exam 2 - Solutions to Heat Equation and Laplace's Equation Problems and more Exams Differential Equations in PDF only on Docsity! Math 412-501 October 20, 2006 Exam 2 Problem 1 (50 pts.) Solve the heat equation in a rectangle 0 < x < π, 0 < y < π, ∂u ∂t = ∂2u ∂x2 + ∂2u ∂y2 subject to the initial condition u(x, y, 0) = (sin 2x + sin 3x) sin y and the boundary conditions u(0, y, t) = u(π, y, t) = 0, u(x, 0, t) = u(x, π, t) = 0. Problem 2 (50 pts.) Solve Laplace’s equation inside a quarter-circle 0 < r < 1, 0 < θ < π/2 (in polar coordinates r, θ) subject to the boundary conditions u(r, 0) = 0, u(r, π/2) = 0, |u(0, θ)| < ∞, u(1, θ) = f(θ). Bonus Problem 3 (40 pts.) Consider a regular Sturm-Liouville eigenvalue problem φ′′ + λφ = 0, φ′(0) = 0, φ′(1) + hφ(1) = 0, where h is a real constant. (i) For what values of h is λ = 0 an eigenvalue? (ii) For what values of h are all eigenvalues positive? (iii) How many negative eigenvalues can this problem have? (iv) Find an equation for positive eigenvalues. (v) Find the asymptotics of λn as n →∞.