Question

The equation of the tangent to the curve $$y = {e^{ - \left| x \right|}}$$   at the point where the curve cuts the line $$x=1$$  is :

A. $$x+y=e$$
B. $$e\left( {x + y} \right) = 1$$
C. $$y+ex=1$$
D. none of these  
Answer :   none of these
Solution :
The point of intersection is $$\left( {1,\,\frac{1}{e}} \right)$$
Around $$x = 1,\,\,\left| x \right| = x$$
$$\eqalign{ & {\text{So, }}y = {e^{ - x}} \cr & \therefore \frac{{dy}}{{dx}} = - {e^{ - x}} \cr & \therefore {\left. {\frac{{dy}}{{dx}}} \right)_{x = 1}} = - {e^{ - 1}} \cr} $$
$$\therefore $$ the equation of the tangent at $$\left( {1,\,\frac{1}{e}} \right)$$  is
$$y - \frac{1}{e} = - \frac{1}{e}\left( {x - 1} \right){\text{ or }}x + ey = 2$$

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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