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Unformatted text preview: MATH 202A HOMEWORK 9 The following assignment is due Wed., Oct. 31. Problem 1 . (a) (Royden problem #43). Let A be an algebra of continuous real valued functions on a compact space X and assume that A separates the points of X . Then either A = C ( X ) or there is a point p X and A = { f C ( X )  f ( p ) = 0 } . Hint: If 1 A , we are done. If f A , which is nowhere zero, then 1 A (see my extra hint at the end of the assignment). If for each x X , there is an f A with f ( x ) 6 = 0, then g A with g > 0 everywhere.] (b) Prove that the set of smooth functions with compact support C c ( R ) is uniformly dense in the space of continuous functions that vanish at infinity C ( R ). Here, a smooth function is one that is infinitely differentiable; the support of a function f is the closure of the set { x R  f ( x ) 6 = 0 } , and the space of functions C ( R ) is the set of all continuous functions f ( x ) on R such that for each > 0 there exists a compact set K R such that  f ( x )  < on K c . Suggestion: Identify C ( R ) with the subspace of C ( S 1 ) of functions vanishing at a point, and apply (a). You will need to build one smooth function with compact support. One way to do this is to show ( x ) = e 1 /x for x > for x is smooth and define ( x ) = (1 x ) (1 + x )....
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This note was uploaded on 04/06/2010 for the course MATH various taught by Professor Tao/analysis during the Spring '10 term at UCLA.
 Spring '10
 tao/analysis
 Algebra

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