Friday, 24 October 2014

real analysis - Using the Law of the Mean (MVT) to prove the inequality $log(1+x)

If x>0, then log(1+x)<x.



My attempt at the proof thus far...



Let f(x)=xlog(1+x), then f(x)=111+x for some μ(0,x) (since x>0)



MVT give us f(x)=f(a)+f(μ)(xa)




So plug in our values we get:



xlog(1+x)=0+(111+μ)(x0)



which we can reduce to



log(1+x)=x1+μ



Now For x1, then 0<μ<1




S0 0<11+μ<1, thus log(1+x)<x



If x>1, then....



So I can see clearly that if x>1 is plugged into x1+μ



then $\log(1+x)

I would appreciate tips hints or proof completions.

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