- #1

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## Homework Statement

k is a real number and [tex]f_{k}(t)=e^{t}-1-t-k\frac{x^{2}}{2}[/tex]

1- Show that : [tex](\forall x\epsilon\mathbb{R}):0\leq e^{x}-1-x[/tex]

2- Show that : [tex](\forall x>0)(\exists k\epsilon\mathbb{R}^{+})(\exists d\epsilon[0,x]):f(x)=f''(d)=0[/tex]

3-Conclude that [tex](\forall x\epsilon\mathbb{R}):|e^{x}-1-x|\leq\frac{x^{2}}{2}e^{|x|}[/tex]

## The Attempt at a Solution

For number 1 i said f(x) =e^x-1-x and f'(x)=e^x-1 so if x >0 than f in increasing and if x<0 f is a decreasing function so f(x)>f(0) in both cases so therefore: that 0<e^x-1-x.

Number 2 I don't know what to do can someone help please??

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