Question

If $$y = \frac{{\left( {a - x} \right)\sqrt {a - x} - \left( {b - x} \right)\sqrt {x - b} }}{{\sqrt {a - x} + \sqrt {x - b} }},$$         then $$\frac{{dy}}{{dx}}$$  wherever it is defined is :

A. $$\frac{{x + \left( {a + b} \right)}}{{\sqrt {\left( {a - x} \right)\left( {x - b} \right)} }}$$
B. $$\frac{{2x - a - b}}{{2\sqrt {a - x} \sqrt {x - b} }}$$  
C. $$ - \frac{{\left( {a + b} \right)}}{{2\sqrt {\left( {a - x} \right)\left( {x - b} \right)} }}$$
D. $$\frac{{2x + \left( {a + b} \right)}}{{2\sqrt {\left( {a - x} \right)\left( {x - b} \right)} }}$$
Answer :   $$\frac{{2x - a - b}}{{2\sqrt {a - x} \sqrt {x - b} }}$$
Solution :
$$\eqalign{ & y = \frac{{{{\left( {a - x} \right)}^{\frac{3}{2}}} + {{\left( {x - b} \right)}^{\frac{3}{2}}}}}{{\sqrt {a - x} + \sqrt {x - b} }} \cr & = \frac{{\left( {\sqrt {a - x} + \sqrt {x - b} } \right)\left( {a - x - \sqrt {a - x} \sqrt {x - b} + x - b} \right)}}{{\sqrt {a - x} + \sqrt {x - b} }} \cr & = a - b - \sqrt {a - x} \sqrt {x - b} \cr & {\text{or }}\frac{{dy}}{{dx}} = \frac{1}{{2\sqrt {a - x} }}\sqrt {x - b} - \frac{1}{{2\sqrt {x - b} }}\sqrt {a - x} \cr & = \frac{{2x - a - b}}{{2\sqrt {a - x} \sqrt {x - b} }} \cr} $$

Releted MCQ Question on
Calculus >> Differentiability and Differentiation

Releted Question 1

There exist a function $$f\left( x \right),$$  satisfying $$f\left( 0 \right) = 1,\,f'\left( 0 \right) = - 1,\,f\left( x \right) > 0$$       for all $$x,$$ and-

A. $$f''\left( x \right) > 0$$   for all $$x$$
B. $$ - 1 < f''\left( x \right) < 0$$    for all $$x$$
C. $$ - 2 \leqslant f''\left( x \right) \leqslant - 1$$    for all $$x$$
D. $$f''\left( x \right) < - 2$$   for all $$x$$
Releted Question 2

If $$f\left( a \right) = 2,\,f'\left( a \right) = 1,\,g\left( a \right) = - 1,\,g'\left( a \right) = 2,$$         then the value of $$\mathop {\lim }\limits_{x \to a} \frac{{g\left( x \right)f\left( a \right) - g\left( a \right)f\left( x \right)}}{{x - a}}$$      is-

A. $$-5$$
B. $$\frac{1}{5}$$
C. $$5$$
D. none of these
Releted Question 3

Let $$f:R \to R$$   be a differentiable function and $$f\left( 1 \right) = 4.$$   Then the value of $$\mathop {\lim }\limits_{x \to 1} \int\limits_4^{f\left( x \right)} {\frac{{2t}}{{x - 1}}} dt$$     is-

A. $$8f'\left( 1 \right)$$
B. $$4f'\left( 1 \right)$$
C. $$2f'\left( 1 \right)$$
D. $$f'\left( 1 \right)$$
Releted Question 4

Let [.] denote the greatest integer function and $$f\left( x \right) = \left[ {{{\tan }^2}x} \right],$$    then:

A. $$\mathop {\lim }\limits_{x \to 0} f\left( x \right)$$     does not exist
B. $$f\left( x \right)$$  is continuous at $$x = 0$$
C. $$f\left( x \right)$$  is not differentiable at $$x =0$$
D. $$f'\left( 0 \right) = 1$$

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Differentiability and Differentiation


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