Question

\[{\rm{Let }}f\left( x \right) = \left| \begin{array}{l} {x^3}\,\,\,\,\,\sin \,x\,\,\,\,\,\cos \,x\\ 6\,\,\,\,\,\,\,\,\,\,\, - 1\,\,\,\,\,\,\,\,\,\,0\\ p\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{p^2}\,\,\,\,\,\,\,\,\,{p^3} \end{array} \right|,\]
where $$p$$ is a constant. Then $$\frac{{{d^3}}}{{d{x^3}}}\left\{ {f\left( x \right)} \right\}$$   at $$x=0$$  is :

A. $$p$$
B. $$p + {p^2}$$
C. $$p + {p^3}$$
D. independent of $$p$$  
Answer :   independent of $$p$$
Solution :
$$\eqalign{ & f\left( x \right) = - {p^3}{x^3} - 6{p^3}.\sin \,x + \left( {6{p^2} + p} \right)\cos \,x \cr & \therefore f'\left( x \right) = - 3{p^3}{x^2} - 6{p^3}.\cos \,x - \left( {6{p^2} + p} \right)\sin \,x \cr & \therefore f''\left( x \right) = - 6{p^3}x + 6{p^3}.\sin \,x - \left( {6{p^2} + p} \right)\cos \,x \cr & \therefore f'''\left( x \right) = - 6{p^3} + 6{p^3}.\cos \,x + \left( {6{p^2} + p} \right)\sin \,x \cr & \therefore f'''\left( 0 \right) = - 6{p^3} + 6{p^3}.1 = 0 = {\text{independent of}}\,{\text{ }}p. \cr} $$

Releted MCQ Question on
Calculus >> Differentiability and Differentiation

Releted Question 1

There exist a function $$f\left( x \right),$$  satisfying $$f\left( 0 \right) = 1,\,f'\left( 0 \right) = - 1,\,f\left( x \right) > 0$$       for all $$x,$$ and-

A. $$f''\left( x \right) > 0$$   for all $$x$$
B. $$ - 1 < f''\left( x \right) < 0$$    for all $$x$$
C. $$ - 2 \leqslant f''\left( x \right) \leqslant - 1$$    for all $$x$$
D. $$f''\left( x \right) < - 2$$   for all $$x$$
Releted Question 2

If $$f\left( a \right) = 2,\,f'\left( a \right) = 1,\,g\left( a \right) = - 1,\,g'\left( a \right) = 2,$$         then the value of $$\mathop {\lim }\limits_{x \to a} \frac{{g\left( x \right)f\left( a \right) - g\left( a \right)f\left( x \right)}}{{x - a}}$$      is-

A. $$-5$$
B. $$\frac{1}{5}$$
C. $$5$$
D. none of these
Releted Question 3

Let $$f:R \to R$$   be a differentiable function and $$f\left( 1 \right) = 4.$$   Then the value of $$\mathop {\lim }\limits_{x \to 1} \int\limits_4^{f\left( x \right)} {\frac{{2t}}{{x - 1}}} dt$$     is-

A. $$8f'\left( 1 \right)$$
B. $$4f'\left( 1 \right)$$
C. $$2f'\left( 1 \right)$$
D. $$f'\left( 1 \right)$$
Releted Question 4

Let [.] denote the greatest integer function and $$f\left( x \right) = \left[ {{{\tan }^2}x} \right],$$    then:

A. $$\mathop {\lim }\limits_{x \to 0} f\left( x \right)$$     does not exist
B. $$f\left( x \right)$$  is continuous at $$x = 0$$
C. $$f\left( x \right)$$  is not differentiable at $$x =0$$
D. $$f'\left( 0 \right) = 1$$

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Differentiability and Differentiation


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