Posted by **ZUkii** on Tuesday, May 29, 2012 at 12:39am.

Evaluate the following

(x+7)dx/x^2+14x+55

- calculus - eh? -
**Steve**, Tuesday, May 29, 2012 at 3:53am
makes no sense as written

better look again and copy it accurately

- calculus -
**Bosnian**, Tuesday, May 29, 2012 at 4:11am
If (x+7)dx/x^2+14x+55

mean

( x + 7 ) dx / ( x ^ 2 + 14 x + 55 )

then substitute :

u = x ^ 2 + 14 x + 5

d u = ( 2 x + 14 ) dx = 2 ( x + 7 ) d x Divide both sides by 2

du / 2 = ( x + 7 ) d x

( x + 7 ) d x = d u / 2

integral of [ ( x + 7 ) dx / ( x ^ 2 + 14 x + 55 ) ] =

integral of [ ( d u / 2 ) / u ) ] =

( 1 / 2 ) integral of ( du / u ) =

( 1 / 2 ) log ( u ) + C =

( 1 / 2 ) log ( x ^ 2 + 14 x + 5 ) + C =

log [ sqrt ( x ^ 2 + 14 x + 5 ) ] + C

Remark :

log is the natural logarithm

( 1 / n ) log ( a ) = log ] ( n - th root ( a ) ]

( 1 / 2 ) log ( a ) = log [ sqrt ( a ) ]

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