Question

Let $$f\left( x \right)$$  be a function defined as follows :
$$f\left( x \right) = \sin \left( {{x^2} - 3x} \right),\,x \leqslant 0;$$      and $$6x + 5{x^2},\,x > 0$$
Then at $$x = 0,\,f\left( x \right)$$

A. has a local maximum
B. has a local minimum  
C. is discontinuous
D. None of these
Answer :   has a local minimum
Solution :
$$\eqalign{ & f\left( 0 \right) = \sin \,0 = 0,\,f\left( {{0^ + }} \right) \to {0^ + } \cr & f\left( {{0^ - }} \right) = \mathop {\lim }\limits_{x \to {0^ - }} \sin \left( {{x^2} - 3x} \right) = \mathop {\lim }\limits_{h \to 0} \sin \left( {{h^2} + 3h} \right) \to {0^ + } \cr & {\text{Thus, }}f\left( {{0^ + }} \right) > f\left( 0 \right){\text{ and }}f\left( {{0^ - }} \right) > f\left( 0 \right) \cr} $$
Hence, $$x = 0$$  is a point of minima.

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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