Question

Let $$f:R \to R$$   is differentiable function and $$f\left( 1 \right) = 4,$$   then the value of $$\mathop {\lim }\limits_{x \to 1} \int\limits_0^{f\left( x \right)} {\frac{{2t\,dt}}{{x - 1}}} $$   is :

A. $$8f'\left( 1 \right)$$  
B. $$4f'\left( 1 \right)$$
C. $$2f'\left( 1 \right)$$
D. $$f'\left( 1 \right)$$
Answer :   $$8f'\left( 1 \right)$$
Solution :
$$\eqalign{ & \mathop {\lim }\limits_{x \to 1} \int\limits_0^{f\left( x \right)} {\frac{{2t}}{{x - 1}}dt} \cr & = \mathop {\lim }\limits_{x \to 1} \frac{1}{{x - 1}}\left[ {{t^2}} \right]_0^{f\left( x \right)} \cr & = \mathop {\lim }\limits_{x \to 1} \frac{{{f^2}\left( x \right) - {f^2}\left( 0 \right)}}{{x - 1}} \cr & = \mathop {\lim }\limits_{x \to 1} \frac{{2f\left( x \right)f'\left( x \right)}}{1}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {{\text{using L'Hospital Rule}}} \right) \cr & = 2f\left( 1 \right)f'\left( 1 \right) \cr & = 8f'\left( 1 \right) \cr} $$

Releted MCQ Question on
Calculus >> Definite Integration

Releted Question 1

The value of the definite integral $$\int\limits_0^1 {\left( {1 + {e^{ - {x^2}}}} \right)} \,dx$$     is-

A. $$ - 1$$
B. $$2$$
C. $$1 + {e^{ - 1}}$$
D. none of these
Releted Question 2

Let $$a,\,b,\,c$$   be non-zero real numbers such that $$\int\limits_0^1 {\left( {1 + {{\cos }^8}x} \right)\left( {a{x^2} + bx + c} \right)dx = } \int\limits_0^2 {\left( {1 + {{\cos }^8}x} \right)\left( {a{x^2} + bx + c} \right)dx.} $$
Then the quadratic equation $$a{x^2} + bx + c = 0$$     has-

A. no root in $$\left( {0,\,2} \right)$$
B. at least one root in $$\left( {0,\,2} \right)$$
C. a double root in $$\left( {0,\,2} \right)$$
D. two imaginary roots
Releted Question 3

The value of the integral $$\int\limits_0^{\frac{\pi }{2}} {\frac{{\sqrt {\cot \,x} }}{{\sqrt {\cot \,x} + \sqrt {\tan \,x} }}dx} $$     is-

A. $$\frac{\pi }{4}$$
B. $$\frac{\pi }{2}$$
C. $$\pi $$
D. none of these
Releted Question 4

For any integer $$n$$ the integral $$\int\limits_0^\pi {{e^{{{\cos }^2}x}}} {\cos ^3}\left( {2n + 1} \right)xdx$$     has the value-

A. $$\pi $$
B. $$1$$
C. $$0$$
D. none of these

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