(g) Consider E=C([0,1]) induced with the uniform norm and consider the line ar form: E→R defined by 4(f) 2(1) = [ ²³ ƒ (1)d² − [ ₁ f(t)dt- f(t)dt, fEE. i. Show that is continuous and calculate |||| ii. Show that if y(f)| = 1 with ||f||∞ = 1, then f(t): = What do you conclude? 1, 0

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Chapter2: Second-order Linear Odes
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part f g ii and iii functionnal analysis
Problem 1. Let E be a real vector space, F be a closed subspace of E, and a € E\F.
Set d(a, F) inf{||ax||; x = F}.
1. Show that if F ha a finite dimension then there exists xo F such that d(x, F) =
||x-xo||.
2. Let be nonzero linear continuous form on E and a € E such that p(a) 0. We
consider F Ker p.
(a) Show that ||||d(a, Ker 4)
|p(a)|
(b) Show that (u+ta)|
||u + ta||
Ker +Ra).
(c) Deduce that |||| =
<
|y(a)|
d(a, kerp)'
|p(a)|
d(a, Ker )
Vu € Ker p. (Hint: Recall that E=
(d) Show that if uo Ker such that d(a, Ker p) = ||a - roll then there exists
To E such that|ro|| = 1 and |(ro)| = ||||-
(e) Let zo E so that oto+ta with v Ker . Suppose that ||zo|| = 1 and
€
(0)|||||. Show that told(a, Ker y) = 1.
(f) Deduce from the previous part that if zo € E such that ||zo|| = 1 and y(x) =
|||| then there exists uo € Ker such that d(a, Ker y) = ||a - xo||-
(g) Consider E= C([0, 1]) induced with the uniform norm and consider the line ar
form: ER defined by
9($) = [*¹ f(t)dt = ['f(t}dt,_ ƒ = E.
i. Show that is continuous and calculate ||||.
ii. Show that if y(f)|=1 with ||f|| = 1, then f(t):
What do you conclude?
[1, 0<t<
-1, <t<1
Transcribed Image Text:Problem 1. Let E be a real vector space, F be a closed subspace of E, and a € E\F. Set d(a, F) inf{||ax||; x = F}. 1. Show that if F ha a finite dimension then there exists xo F such that d(x, F) = ||x-xo||. 2. Let be nonzero linear continuous form on E and a € E such that p(a) 0. We consider F Ker p. (a) Show that ||||d(a, Ker 4) |p(a)| (b) Show that (u+ta)| ||u + ta|| Ker +Ra). (c) Deduce that |||| = < |y(a)| d(a, kerp)' |p(a)| d(a, Ker ) Vu € Ker p. (Hint: Recall that E= (d) Show that if uo Ker such that d(a, Ker p) = ||a - roll then there exists To E such that|ro|| = 1 and |(ro)| = ||||- (e) Let zo E so that oto+ta with v Ker . Suppose that ||zo|| = 1 and € (0)|||||. Show that told(a, Ker y) = 1. (f) Deduce from the previous part that if zo € E such that ||zo|| = 1 and y(x) = |||| then there exists uo € Ker such that d(a, Ker y) = ||a - xo||- (g) Consider E= C([0, 1]) induced with the uniform norm and consider the line ar form: ER defined by 9($) = [*¹ f(t)dt = ['f(t}dt,_ ƒ = E. i. Show that is continuous and calculate ||||. ii. Show that if y(f)|=1 with ||f|| = 1, then f(t): What do you conclude? [1, 0<t< -1, <t<1
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