Question

Let $$x$$ be a number which exceeds its square by the greatest possible quantity. Then $$x$$ is equal to :

A. $$\frac{1}{2}$$  
B. $$\frac{1}{4}$$
C. $$\frac{3}{4}$$
D. none of these
Answer :   $$\frac{1}{2}$$
Solution :
$$y = x - {x^2}$$   where $$y$$ is the greatest difference.
$$\eqalign{ & \frac{{dy}}{{dx}} = 1 - 2x \cr & \therefore \frac{{dy}}{{dx}} = 0 \Rightarrow x = \frac{1}{2} \cr} $$
Again, $$\frac{{{d^2}y}}{{d{x^2}}} = - 2$$
$$\therefore \,y$$   is the maximum at $$x = \frac{1}{2}$$

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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