Question:

If '' > 0$ for all $

Updated On: Jun 14, 2022
  • $' (1) \leq 0$
  • $0 < ' 1 = \frac{1}{2}$
  • $\frac{1}{2} < ' 1 = 1 $
  • $' (1) > 1$
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The Correct Option is D

Solution and Explanation

Let $h ( x )= f ( x )- x$
$h \left(\frac{1}{2}\right)=0= h (1)$
$\Rightarrow h '(\alpha)=0$ for some $\alpha \in(0,1)$ by rolle's theorem
$f'(\alpha)=1$
as $f'(x)>0 $
$\Rightarrow f(x)$ is increasing
$\therefore f (1)> f '(\alpha)$
$f '(1)>1$
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Questions Asked in JEE Advanced exam

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Concepts Used:

Application of Derivatives

Various Applications of Derivatives-

Rate of Change of Quantities:

If some other quantity ‘y’ causes some change in a quantity of surely ‘x’, in view of the fact that an equation of the form y = f(x) gets consistently pleased, i.e, ‘y’ is a function of ‘x’ then the rate of change of ‘y’ related to ‘x’ is to be given by 

\(\frac{\triangle y}{\triangle x}=\frac{y_2-y_1}{x_2-x_1}\)

This is also known to be as the Average Rate of Change.

Increasing and Decreasing Function:

Consider y = f(x) be a differentiable function (whose derivative exists at all points in the domain) in an interval x = (a,b).

  • If for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≤ f(x2); then the function f(x) is known as increasing in this interval.
  • Likewise, if for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≥ f(x2); then the function f(x) is known as decreasing in this interval.
  • The functions are commonly known as strictly increasing or decreasing functions, given the inequalities are strict: f(x1) < f(x2) for strictly increasing and f(x1) > f(x2) for strictly decreasing.

Read More: Application of Derivatives