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Let-f-1-5-R-be-defined-by-f-x-6-x-1-Show-that-f-has-a-unique-fixed-point-and-find-it-




Question Number 125814 by Tanuidesire last updated on 14/Dec/20
Let f:[1,5]→R be defined by f(x)=(6/(x+1)). Show that f has a unique fixed point and find it.
Letf:[1,5]Rbedefinedbyf(x)=6x+1.Showthatfhasauniquefixedpointandfindit.
Answered by Olaf last updated on 14/Dec/20
f strictly decreases and :  f(1) = (6/(1+1)) = 3  f(5) = (6/(5+1)) = 1  f([1,5]) = [1,3] ⊆ [1,5]  and :  f(x) = x ⇔ x^2 +x−6 = 0  ⇔ x = ((−1±(√(1−4(1)(−6))))/2) = −3 or 2  Only x = 2 is included in [1,5].  ⇒ S = { 2 }.
fstrictlydecreasesand:f(1)=61+1=3f(5)=65+1=1f([1,5])=[1,3][1,5]and:f(x)=xx2+x6=0x=1±14(1)(6)2=3or2Onlyx=2isincludedin[1,5].S={2}.

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