1 S(x) = É +n²x"
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Q4 Real analysis by Walton rudin chp#7

Transcribed Image Text:is self-adjoint, we see that u e AR. If x, # x2, there exists feA such
that f(x1) = 1, f(x2) = 0; hence 0 = u(x2) # u(x1) = 1, which shows that
AR separates points on K. If x e K, then g(x) +0 for some g eA, and
there is a complex number 2 such that ig(x) > 0; if f = ig, f = u + iv, it
follows that u(x) > 0; hence AR vanishes at no point of K.
Thus AR satisfies the hypotheses of Theorem 7.32. It follows that
every real continuous function on K lies in the uniform closure of AR,
hence lies in 3. If f is a complex continuous function on K, f = u +iv,
then u e B, v E ®, hence f E B. This completes the proof.
EXERCISES
1. Prove that every uniformly convergent sequence of bounded functions is uni-
formly bounded.
2. If {f) and {g.) converge uniformly on a set E, prove that {f.+ gn} converges
uniformly on E, If, in addition, {f) and {g.) are sequences of bounded functions,
prove that (fag,) converges uniformly on E.
3. Construct sequences {f.), {gn} which converge uniformly on some set E, but such
that {fagn) does not converge uniformly on E (of course, {fng.} must converge on
E).
4. Consider
f(x) =
For what values of x does the series converge absolutely ? On what intervals does
it converge uniformly? On what intervals does it fail to converge uniformly? Is f
continuous wherever the series converges? Is f bounded?
166 PRINCIPLES OF MATHEMATICAL ANALYSIS
5. Let
sin²
(n+1
Show that {f} converges to a continuous function, but not uniformly. Use the
series E f. to show that absolute convergence, even for all x, does not imply uni-
form convergence.
6. Prove that the series
converges uniformly in every bounded interval, but does not converge absolutely
for any value of x.
7. For n= 1, 2, 3, ..., x real, put
Show that {f.} converges uniformly to a function f, and that the equation
f'(x)= lim f.(x)
is correct if x #0, but false if x=0.
8. If
(o
(xS0),
(x>0),
I(x) =
if (xn) is a sequence of distinct points of (a, b), and if E c.| converges, prove that
the series
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