Math 445 and 447 - PRACTICE FINAL EXAM V1 Part D: Long Answer. Math 445 students: Complete 7 problems from the following list. Math 447 students: Complete 8 problems from the following list. 1. Show that a non-empty closed subset S of a compact metric space X is compact. HINT: Sequential compactness is easier to deal with. 2. If d is a metric on X, show that d1(x, y) = d(x,y) 1+d(x,y) is also a metric on X. 3. Suppose that W is a subspace of a normed linear space V . Show that the closure W is also a subspace. 4. Define a linear transformation T : C([0, 1])→ C([0, 1]) by Tf(x) = ∫ x 0 f(t)g(t)dt where g is a continuous function [0, 1]. Show that ‖T‖ ≤ ‖g‖∞. 5. Show that fn(x) = xne −nx converges pointwise to zero but not uniformly on [0,∞). 6. Let F be a compact subset of C([0, 1]). Show that there is a function g ∈ F such that∫ 1 0 g(x)dx ≥ ∫ 1 0 f(x)dx for all f ∈ F . HINT: Show that the function sending f to ∫ 10 f is continuous in the appropriate context, and therefore attains its maximum. 7. Show that f(x, y) = x 2y √ x2+y2 x4+y2 (x, y) 6= (0, 0) 0 (x, y) = (0, 0) is continuous at (0, 0) and that Dvf(0, 0) exists for all unit vectors v. 8. Show that f in problem 7 is not differentiable at (0, 0). 9. Suppose f : Rn → R is differentiable and f has a local minimum at x0. Show that Df(x0) = 0. 10. Consider the following non-linear equations: x4 + y2 − 2z + w = 3 x− 2y + w4 = 0 Determine the points (x0, y0, z0, w0) for which the hypotheses of the implicit function theorem is satisfied. Page 1 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 2 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 3 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 4 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 5 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 6 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 7 Math 445 and 447 - PRACTICE FINAL EXAM V1 Extra Space: Page 8
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