While this is

Calculus Level 3

3 37 1 + x + x 2 1 + x 2 d x = A \displaystyle \int _{ 3 }^{ 37 }{ \frac { 1+x+{ x }^{ 2 } }{ 1+{ x }^{ 2 } } dx=A }

Find A \left\lfloor A \right\rfloor .


The answer is 36.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

3 solutions

Rishabh Jain
Feb 25, 2016

Or this could be done like this !! ;-) I = 3 37 1 + x + x 2 1 + x 2 d x \mathfrak{I}=\displaystyle \int _{ 3 }^{ 37} \frac { 1+x+{ x }^{ 2 } }{ 1+{ x }^{ 2 } } dx = 3 37 ( 1 + x 1 + x 2 ) d x =\displaystyle \int _{ 3 }^{ 37 }( 1+ \frac { x}{1+x^2})dx = 34 + 3 37 1 2 ( d ( 1 + x 2 ) 1 + x 2 ) =34+\displaystyle \int _{ 3 }^{ 37 } \frac{1}{2}(\frac { d(1+x^2)}{1+x^2}) = 34 + 1 2 ( ln ( 1370 10 ) ) 36.46 =34+\dfrac{1}{2}(\ln (\frac{1370}{10}))\approx 36.46 Hence A = 36 \left\lfloor A \right\rfloor =\boxed{\large 36}

Chew-Seong Cheong
Feb 25, 2016

A = 3 37 1 + x + x 2 1 + x 2 d x Let x = tan θ d x = sec 2 θ d θ = tan 1 3 tan 1 37 ( 1 + tan θ + tan 2 θ ) sec 2 θ sec 2 θ d θ = tan 1 3 tan 1 37 ( tan θ + sec 2 θ ) d θ = tan 1 3 tan 1 37 sin θ cos θ d θ + tan 1 3 tan 1 37 sec 2 θ d θ = 1 10 1 1370 d cos θ cos θ + 3 37 d tan θ d θ = [ ln ( cos θ ) ] 1 1370 1 10 + [ tan θ ] 3 37 = ln 137 2 + 34 36.460 \begin{aligned} A & = \int_3^{37} \frac{1+x+x^2}{1+x^2} \space dx \quad \quad \small \color{#3D99F6}{\text{Let } x = \tan \theta \quad \Rightarrow dx = \sec^2 \theta \space d\theta} \\ & = \int_{\tan^{-1} 3}^{\tan^{-1} 37} \frac{\left(1+\tan \theta + \tan^2 \theta \right) \sec^2 \theta}{\sec^2 \theta} \space d\theta \\ & = \int_{\tan^{-1} 3}^{\tan^{-1} 37} \left(\tan \theta + \sec^2 \theta \right) \space d\theta \\ & = \int_{\tan^{-1} 3}^{\tan^{-1} 37} \frac{\sin \theta}{\cos \theta} \space d\theta + \int_{\tan^{-1} 3}^{\tan^{-1} 37} \sec^2 \theta \space d\theta \\ & = - \int_{\frac{1}{\sqrt{10}}}^{\frac{1}{\sqrt{1370}}} \frac{d \cos \theta}{\cos \theta} + \int_3^{37} d \tan \theta \space d\theta \\ & = \left[\ln (\cos \theta) \right]^{\frac{1}{\sqrt{10}}}_{\frac{1}{\sqrt{1370}}} + \left[ \tan \theta \right]_3^{37} \\ & = \frac{\ln 137}{2} + 34 \approx 36.460 \end{aligned}

A = 36 \Rightarrow \lfloor A \rfloor = \boxed{36}

Jose Sacramento
Feb 26, 2016

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...