Question

Let $$f\left( x \right) = {x^3} - 6{x^2} + 12x - 3.$$     Then at $$x = 2,\,f\left( x \right)$$   has :

A. a maximum
B. a minimum
C. both a maximum and a minimum
D. neither a maximum nor a minimum  
Answer :   neither a maximum nor a minimum
Solution :
$$\eqalign{ & f'\left( x \right) = 3{x^2} - 12x + 12 = 3{\left( {x - 2} \right)^2} \cr & \therefore \,f'\left( 2 \right) = 0\,; \cr & f'\left( {2 - \in } \right) = 3{ \in ^2} > 0\,; \cr & f'\left( {2 + \in } \right) = 3{ \in ^2} > 0 \cr} $$
Hence, $$f\left( x \right)$$  has neither a maximum nor a minimum at $$x=2.$$

Releted MCQ Question on
Calculus >> Application of Derivatives

Releted Question 1

If  $$a + b + c = 0,$$    then the quadratic equation $$3a{x^2}+ 2bx + c = 0$$     has

A. at least one root in $$\left[ {0, 1} \right]$$
B. one root in $$\left[ {2, 3} \right]$$  and the other in $$\left[ { - 2, - 1} \right]$$
C. imaginary roots
D. none of these
Releted Question 2

$$AB$$  is a diameter of a circle and $$C$$ is any point on the circumference of the circle. Then

A. the area of $$\Delta ABC$$  is maximum when it is isosceles
B. the area of $$\Delta ABC$$  is minimum when it is isosceles
C. the perimeter of $$\Delta ABC$$  is minimum when it is isosceles
D. none of these
Releted Question 3

The normal to the curve $$x = a\left( {\cos \theta + \theta \sin \theta } \right),y = a\left( {\sin \theta - \theta \cos \theta } \right)$$        at any point $$'\theta '$$ is such that

A. it makes a constant angle with the $$x - $$axis
B. it passes through the origin
C. it is at a constant distance from the origin
D. none of these
Releted Question 4

If $$y = a\ln x + b{x^2} + x$$     has its extremum values at $$x = - 1$$  and $$x = 2,$$  then

A. $$a = 2,b = - 1$$
B. $$a = 2,b = - \frac{1}{2}$$
C. $$a = - 2,b = \frac{1}{2}$$
D. none of these

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