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Math Help - another integral

  1. #1
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    another integral

    I understand how the book solved the integral but don't get how they got an answer of infinity.

    \int_{0}^{\pi/2} tan x~dx=\lim_{b\to(\pi/2)^-}ln |secx|(from~0~to~b)=\infty. I get an answer of 0. \lim_{b\to(\pi/2)^-}[ln|secb|-ln|sec0|]=0-0=0

    What am I doing wrong?
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  2. #2
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    Quote Originally Posted by Possible actuary View Post
    I understand how the book solved the integral but don't get how they got an answer of infinity.

    \int_{0}^{\pi/2} tan x~dx=\lim_{b\to(\pi/2)^-}ln |secx|(from~0~to~b)=\infty. I get an answer of 0. \lim_{b\to(\pi/2)^-}[ln|secb|-ln|sec0|]=0-0=0

    What am I doing wrong?
    sec \left ( \frac{\pi}{2} \right ) = \frac{1}{cos \left ( \frac{\pi}{2} \right ) } \to \frac{1}{0}
    which most people take to be infinite.

    -Dan
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