For all $x \in(0,1)$
Answer & explanation
Correct answer: option 2
Consider the function
$f(x)=e^x-(1+x)$
$\Rightarrow f'(x)=e^x-1$
$\Rightarrow f'(x)>0 \text { for } x \in(0,1)$
⇒ f(x) is increasing on (0, 1)
$\Rightarrow f(x)>f(0) $ for all $ x \in(0,1)$
$\Rightarrow e^x-(1+x)>$ for all $ x \in(0,1)$
$\Rightarrow e^x>1+x $ for all $ x \in(0,1)$
Thus, option (a) is not correct.
Let $g(x)=\log _e(1+x)-x, x \in(0,1)$. Then,
$g'(x)=\frac{1}{1+x}-1=-\frac{x}{1+x}<0$ for all $x \in(0,1)$
⇒ g(x) is decreasing on (0, 1)
$\Rightarrow g(x)<g(0)$ for all $x \in(0,1)$
$\Rightarrow \log _e(1+x)-x<0$ for all $x \in(0,1)$
$\Rightarrow \log _e(1+x)<x$ for all $x \in(0,1)$
Thus, option (b) is correct.
Similarly, it can be shown that options (c) and (d) do not hold.