Question

Let $$f\left( x \right) = \cos \,\pi x + 10x + 3{x^2} + {x^3},\, - 2 \leqslant x \leqslant 3.$$          The absolute minimum value of $$f\left( x \right)$$  is :

A. 0
B. $$-15$$  
C. $$3 - 2\pi $$
D. none of these
Answer :   $$-15$$
Solution :
$$\eqalign{ & f\left( x \right) = \cos \,\pi x + 10x + 3{x^2} + {x^3} \cr & f'\left( x \right) = - x\,\sin \,\pi x + 10 + 6x + 3{x^2} \cr & f'\left( x \right) = 3{x^2} + 6x = 10 - x\,\sin \,\pi x \cr & f'\left( x \right) = 3{\left( {{x^2} + 1} \right)^2} + 7 - \pi \,\sin \,\pi x \cr & f'\left( x \right) > 0 \cr & f\left( x \right){\text{ is an }} \uparrow {\text{ function}} \cr & f\left( { - 2} \right) = \cos \left( { - 2,\,\pi } \right) + \left( { - 20} \right) + 12 + \left( { - 8} \right) \cr & = 1 - 20 + 12 - 8 \cr & = - 15 \cr} $$

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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