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Dead astern to MA_598R_pweigel_Summer_2009_Lecture_7



Judgment Day

1. You need absolute values everywhere. No points deducted, since it's clear you understand what you're doing, but it's sloppy to the point where you might offend a grader. POINTS: 1/1

2. Good. POINTS: 2/2

3. Good. POINTS: 3/3

4. You have to remind the reader that $ L^2(I) \subset L^1(I) $. I know what you're doing, but the grader might not. POINTS: 4/4

5. Good. POINTS: 5/5

6. You need continuity of $ \hat{f} $! It seems implicit in the proof, especially since we already did that question, but this would be marked wrong on a qual. POINTS: 5.9/6

7. Good. POINTS: 6.9/7

11. The line involving the MVT is a mess. I would have no idea what you were talking about. Also, the $ \displaystyle\lim_{h \rightarrow 0^+} $ is superfluous (and wrong). A fix would be that there exists $ \eta_h $ such that $ 0< |\eta_h|< |h| $. You also need to cite Fubini/Tonelli when you interchange products. Full points awarded, however. POINTS: 7.9/11

13. a) This one can't be saved. The definition of $ ||\hat{f}||_{\infty} $ is wrong, and you need that $ \hat{f} $ is continuous to conclude that $ ||\hat{f}||_{\infty} = \sup \{ |\hat{f}(x)| \} $.

   b) As noted, the inverse fourier transform is only equal a.e. to f.  Needs more work.

POINTS: 7.9/13

14. The change of variables is not correct. You need to replace $ x $ with $ Ax $. Then $ A^T A x = x $ since $ A $ is orthogonal. POINTS: 8.9/14

TOTAL POINTS: 8.9

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