Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Applications of Derivatives

Question:

Let $f, g, h$ be real valued functions defined on the interval $[0,1]$ by $f(x)=e^{x^2}+e^{-x^2}, g(x)=x e^{x^2}+e^{-x^2}$ and $h(x)=x^2 e^{x^2}+e^{-x^2}$. If $a, b$ and $c$ denote respectively, the absolute maximum of $f, g$ and $h$ on $[0,1]$, then

Options:

$a=b$ and $c \neq b$

$a=c$ and $a \neq b$

$a \neq b$ and $c \neq b$

$a=b=c$

Correct Answer:

$a=b=c$

Explanation:

For any $x \in[0,1]$, we have

$x^2 \leq x \leq 1$

$\Rightarrow x^2 e^{x^2} \leq x e^{x^2} \leq e^{x^2}$

$\Rightarrow e^{-x^2}+x^2 e^{x^2} \leq e^{-x^2}+x e^{x^2} \leq e^{-x^2}+e^{x^2}$

$\Rightarrow h(x) \leq g(x) \leq f(x)$

Now, $f(x)=e^{x^2}+e^{-x^2}$

$\Rightarrow f^{\prime}(x)=2 x\left(e^{x^2}-e^{-x^2}\right)>0$ for all $x \in(0,1]$

⇒ f(x) is increasing on (0,1]

⇒ f(1) is the maximum value of f(x) on [0, 1]

$\Rightarrow a=e+e^{-1}$

Also, $f(1)=g(1)=h(1)=e+e^{-1}$

∴  $a=b=c=e+e^{-1}$