Exercise 6.7.9

(a)
Find a counterexample which shows that WAT is not true if we replace the closed interval [ a , b ] with the open interval ( a , b ) .
(b)
What happens if we replace [ a , b ] with the closed set [ a , ) . Does the theorem still hold?

Answers

(a)
1 x over ( 0 , 1 ) , since 1 x is unbounded while any approximating polynomial must be bounded over ( 0 , 1 ) .
(b)
e x , since exponentials grow faster than polynomials, and therefore the difference between e x and any polynomial is unbounded over [ 0 , ) .
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2022-01-27 00:00
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