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Posted by on Sunday, August 24, 2008 at 9:11pm.

Find the length of the arc formed by
y = (1/8)(4x^2-2ln(x)) from x=4 to x=8.

I found the derivative of the function and got y'= x-(1/4x)

Where I'm lost now is after plugging it into the arc length equation: integral of sqrt(1+(x-(1/4x))^2). Squaring the derivative yields me sqrt(1+x^2+1/16x-1/2). Help please.

  • calculus - , Sunday, August 24, 2008 at 9:47pm

    I got sqrt [ 1 + x^2 -(1/2) + 1/(16x^2) ]
    which is
    sqrt [ x^2 + (1/2) +1/(16x^2) ]
    BUT
    x^2 + (1/2) + 1/(16x^2) = [x+ 1/(4x)]^2
    ok ?

  • calculus - , Sunday, August 24, 2008 at 10:12pm

    Oh yes, sorry, I merely had a typo. I had the same result as you. What I'm confused about is what to do from that point on.

  • calculus - , Monday, August 25, 2008 at 3:50am

    well, the sqrt of that is just
    x + (1/4)(1/x)
    integral of that is
    (1/2) x^2 + (1/4) ln x

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