1.Relation and Function
hard

Let $f : R \rightarrow R$ be a function defined by $f ( x )=$ $\log _{\sqrt{m}}\{\sqrt{2}(\sin x-\cos x)+m-2\}$, for some $m$, such that the range of $f$ is $[0,2]$. Then the value of $m$ is $............$

A

$5$

B

$3$

C

$2$

D

$4$

(JEE MAIN-2023)

Solution

Since,

$-\sqrt{2} \leq \sin x-\cos x \leq \sqrt{2}$

$\therefore-2 \leq \sqrt{2}(\sin x-\cos x) \leq 2$

$\quad \text { Assume } \sqrt{2}(\sin x-\cos x)=k)$

$-2 \leq k \leq 2 \quad \ldots( i )$

$f(x)=\log _{\sqrt{m}}( k + m -2)$

$\text { Given, }$

$0  \leq f( x ) \leq 2$

$0 \leq \log _{\sqrt{ m }}( k + m -2) \leq 2$

$\leq k + m -2 \leq m$

$- m +3 \leq k \leq 2 \ldots \text { (ii) }$

From eq. $(i)$ and $(ii)$, we get $- m +3=-2$

$\Rightarrow m=5$

Standard 12
Mathematics

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