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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