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单词 ProofOfBernoullisInequality
释义

proof of Bernoulli’s inequality


Let I be the interval (-1,) andf:I the function defined as:

f(x)=(1+x)α-1-αx

with α{0,1} fixed.Then f is differentiableMathworldPlanetmathPlanetmath and its derivativeMathworldPlanetmathPlanetmath is

f(x)=α(1+x)α-1-α, for all xI,

from which it follows that f(x)=0x=0.

  1. 1.

    If 0<α<1 then f(x)<0 for all x(0,)and f(x)>0 for all x(-1,0) which means that 0 is aglobal maximumMathworldPlanetmath point for f.Thereforef(x)<f(0) for all xI{0}which means that(1+x)α<1+αx for all x(-1,0).

  2. 2.

    If α[0,1] then f(x)>0 for all x(0,)and f(x)<0 for all x(-1,0) meaning that 0 is a globalminimum point for f.This implies thatf(x)>f(0) for all xI{0}which means that(1+x)α>1+αx for all x(-1,0).

Checking that the equality is satisfied for x=0 or for α{0,1} ends the proof.

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更新时间:2025/5/4 6:54:31