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5. Continuity and Differentiation
hard
Let $f$ be any function defined on $R$ and let it satisfy the condition
$|f( x )-f( y )| \leq\left|( x - y )^{2}\right|, \forall( x , y ) \in R$ If $f(0)=1,$ then
A
$f(x)$ can take any value in $R$
B
$f(x)< 0, \forall \,x \in R$
C
$f( x )=0, \forall \, x \in R$
D
$f( x )>0, \forall \, x \in R$
(JEE MAIN-2021)
Solution
$\left|\frac{f(x)-f(y)}{(x-y)}\right| \leq|(x-y)|$
$x-y=h$ let $\Rightarrow x=y+h$
$\lim _{x \rightarrow 0}\left|\frac{f(y+h)-f(y)}{h}\right| \leq 0$
$\Rightarrow\left|f^{\prime}( y )\right| \leq 0 \Rightarrow f^{\prime}( y )=0$
$\Rightarrow f( y )= k ($ constant $)$
and $f(0)=1$ given
So, $f(y)=1 \Rightarrow f(x)=1$
Standard 12
Mathematics