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Question Number 30436 by abdo imad last updated on 22/Feb/18
let ϕ(x)=1−2^(1−x)   prove that  ϕ(x)=(x−1)ln2 −(((ln2)^2 )/2)(x−1)^2  +o((x−1)^2 ).
letφ(x)=121xprovethatφ(x)=(x1)ln2(ln2)22(x1)2+o((x1)2).
Commented by prof Abdo imad last updated on 22/Feb/18
x→1
x1
Answered by sma3l2996 last updated on 24/Feb/18
2^t =e^(tln(2)) =1+tln(2)+(((tln2)^2 )/(2!))+o(t^2 )  so  2^(1−x) =1+(1−x)ln(2)+(((ln2)^2 )/2)(1−x)^2 +o((1−x)^2 )  1−2^(1−x) =−(1−x)ln(2)−(((ln2)^2 )/2)(1−x)^2 +o((x−1)^2 )  ϕ(x)=(x−1)ln(2)−(((ln2)^2 )/2)(x−1)^2 +o((x−1)^2 )
2t=etln(2)=1+tln(2)+(tln2)22!+o(t2)so21x=1+(1x)ln(2)+(ln2)22(1x)2+o((1x)2)121x=(1x)ln(2)(ln2)22(1x)2+o((x1)2)φ(x)=(x1)ln(2)(ln2)22(x1)2+o((x1)2)

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