Gujarati
5. Continuity and Differentiation
normal

मान लीजिए कि $f: R \rightarrow R$ अभिकलनीय फलन $(differentiable\,functon)$ इस प्रकार है कि किन्हीं $a < b$ के लिए $f(a)=0=f(b)$ और $f^{\prime}(a) f^{\prime}(b) > 0$ है। अंतराल $(interval$;' $( a , b )$ में $f( x )$ के मूलों $(roots)$ की न्यूनतम संख्या क्या है ?

A

$3$

B

$2$

C

$1$

D

$0$

(KVPY-2010)

Solution

(b)

Given,

$f: R \rightarrow R$ be a differentiable function in $(a, b)$

and $\quad f(a)=f(b)=0, a < b$

and $f^{\prime}(a) f^{\prime}(b) > 0$

Since, $f^{\prime}(a) f^{\prime}(b) > 0$.

$\therefore f^{\prime}(a)$ and $f^{\prime}(b)$ both are positive or negative when both are positive then at least one root. $f^{\prime}(x)=0$ lie in interval, also when both are negative then at least one root lie in the interval.

[by Rolle's theorem]

$\therefore$ Minimum number of roots are $2$.

Standard 12
Mathematics

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