Expert: Paul Klarreich - 5/20/2008

Question
Hi Paul,

I need some help with this problem because I keep getting the wrong answer and I can't figure out what I did wrong. Hope you can clarify it for me. :-)

EVALUATE THE INTEGRAL
  1/6       1
 S       -------  dx
  0     (1-9x)^1/2  

The answer I keep getting is: 0.52359. However, the right answer is: Pi/18.

Answer
Questioner:   Caroline
Category:  Calculus
Private:  No
 
Subject:  Inverse Trig Functions and Integration
Question:  Hi Paul,

I need some help with this problem because I keep getting the wrong answer and I can't figure out what I did wrong. Hope you can clarify it for me. :-)

EVALUATE THE INTEGRAL
 1/6       1
S       -------  dx
 0     (1-9x)^1/2  

The answer I keep getting is: 0.52359. However, the right answer is: Pi/18.
.................................
Hi, Caroline,

You wrote:  
 
The answer I keep getting is: 0.52359. However, the right answer is: Pi/18.

Very funny.  Isn't Pi/18 = 0.52359??
(Actually, it rounds to 0.52360)

Also:  Did you mean to write;

{  1/6       1
|       --------------  dx
}  0     (1-9x^2)^1/2  

because the integral you wrote:

{  1/6       1
|       --------------  dx
}  0     (1-9x)^1/2  

is undefined at  x = 1/6
[ 1 - 9(1/6) = 1 - 3/2 = -1/2]


Note: If you want me to help with: "and I can't figure out what I did wrong"  you will have to show me just what you did.  I can't find a mistake I cannot see, so send all the work, not just the answer.