Question

If the normal to the curve $$y = f\left( x \right)$$  at the point (3, 4) makes an angle $$\frac{{3\pi }}{4}$$ with the positive $$x$$-axis, then $$f'\left( 3 \right) = $$

A. $$ - 1$$
B. $$ - \frac{3}{4}$$
C. $$\frac{4}{3}$$
D. 1  
Answer :   1
Solution :
$$\eqalign{ & {\text{Slope of tangent }}y = f\left( x \right){\text{ is }}\frac{{dy}}{{dx}} = f'{\left( x \right)_{\left( {3,4} \right)}} \cr & {\text{Therefore, slope of normal}} = - \frac{1}{{f'{{\left( x \right)}_{\left( {3,4} \right)}}}} = - \frac{1}{{f'\left( 3 \right)}} \cr & {\text{but }} - \frac{1}{{f'\left( 3 \right)}} = \tan \left( {\frac{{3\pi }}{4}} \right){\text{ }}\left( {{\text{given}}} \right) \cr & {\text{or}}\, - \frac{1}{{f'\left( 3 \right)}} = \tan \left( {\frac{\pi }{2} + \frac{\pi }{4}} \right) = - 1 \Rightarrow f'\left( 3 \right) = 1 \cr} $$

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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