Calculus

Calculus Level 4

The value of

0 ( x 2 + 4 ) ln x x 2 + 16 d x \int_0^{\infty}\frac{(x^2+4)\ln x}{x^2+16}dx

can be expressed as π k 2 ln 2. \frac{\pi}{k\sqrt{2}}\ln 2. Find the value of k . k.


The answer is 2.

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.

1 solution

Shubham Raj
Nov 23, 2014

put x=2t so u will get half of integrand from 0 to infinity [(t^2+1)/(t^4+1)]* ln(2t) dt . now u cn split ln(2t)dt as ln2+lnt . the first term you cn evaluate you will get{ pie/(2 root of 2)} ln2 and second term u cn solve u will get 0.

1 2 0 t 2 + 1 t 4 + 1 ln ( 2 t ) d t = 1 2 0 t 2 + 1 t 4 + 1 ln 2 d t + 1 2 0 t 2 + 1 t 4 + 1 l n t d t = Π 2 2 ln 2 + 0. \frac { 1 }{ 2 } \int _{ 0 }^{ \infty }{ \frac { { t }^{ 2 }+1 }{ { t }^{ 4 }+1 } } \ln { (2t)\quad dt\quad =\quad \frac { 1 }{ 2 } } \int _{ 0 }^{ \infty }{ \frac { { t }^{ 2 }+1 }{ { t }^{ 4 }+1 } } \ln { 2dt+\frac { 1 }{ 2 } } \int _{ 0 }^{ \infty }{ \frac { { t }^{ 2 }+1 }{ { t }^{ 4 }+1 } } lnt\quad dt\quad \\ \\ =\frac { \Pi }{ 2\sqrt { 2 } } \ln { 2 } +0.

sorry for not writing the solution properly. I still dont know how to format properly.

To display the Latex, you should use \ ( Latex code \ ) \backslash ( \text{ Latex code } \backslash) . You used /( and /) instead.

I have edited your solution, so you can refer to it.

Calvin Lin Staff - 6 years, 6 months ago

Log in to reply

thnks for letting me know i will modify its soon

Shubham Raj - 6 years, 6 months ago

Looking at your solution, I believe that you want the denominator of the integrand to be x 4 + 16 x^4 + 16 ? It currently is x 2 + 16 x^2 + 16 .

Please let me know how you want to fix this.

Calvin Lin Staff - 6 years, 6 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...