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Question Number 193247 by mokys last updated on 08/Jun/23
if f(x) = ((ax+1)/(x+b)) find f^( 100) (x) and f^(101) (x) ?
iff(x)=ax+1x+bfindf100(x)andf101(x)?
Answered by aba last updated on 08/Jun/23
f(x)=((ax+1)/(x+b))=a+((1−ab)/(x+b))  f^2 (x)=fof(x)=f(a+((1−ab)/(x+b)))=a+((1−ab)/(f(x)+b))  f^3 (x)=f^2 of(x)=f^2 (a+((1−ab)/(x+b)))=a+((1−ab)/(f(a+((1−ab)/(x+b)))+b))=a+((1−ab)/(a+((1−ab)/(f(x)+b))+b))=a+((1−ab)/(f^2 (x)+b))  f^k (x)=a+((1−ab)/(f^(k−1) (x)+b)), ∀ k≥2  ⇓  f^(100) (x)=a+((1−ab)/(f^(99) (x)+b))    f^(101) (x)=a+((1−ab)/(f^(100) (x)+b))
f(x)=ax+1x+b=a+1abx+bf2(x)=fof(x)=f(a+1abx+b)=a+1abf(x)+bf3(x)=f2of(x)=f2(a+1abx+b)=a+1abf(a+1abx+b)+b=a+1aba+1abf(x)+b+b=a+1abf2(x)+bfk(x)=a+1abfk1(x)+b,k2f100(x)=a+1abf99(x)+bf101(x)=a+1abf100(x)+b
Answered by aba last updated on 09/Jun/23
f^k (x)=a+((1−ab)/(f^(k−1) (x)+b)), ∀k≥2  it is true for k=2. then assume true for k and prove that it is true for k+1  f^(k+1) (x)=f^k of(x)=f^k (f(x))=a+((1−ab)/(f^(k−1) (f(x))+b))=a+((1−ab)/(f^k (x)+b))  ∀k≥2 , f^k (x)=a+((1−ab)/(f^(k−1) (x)+b))
fk(x)=a+1abfk1(x)+b,k2itistruefork=2.thenassumetrueforkandprovethatitistruefork+1fk+1(x)=fkof(x)=fk(f(x))=a+1abfk1(f(x))+b=a+1abfk(x)+bk2,fk(x)=a+1abfk1(x)+b

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