A calculus problem by Aly Ahmed

Calculus Level 3

0 1 x 2 + 5 x 2 16 d x = ? \int_0^1 \dfrac{x^2+5}{x^2-16} \, dx = \, ?


The answer is -0.3409.

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2 solutions

Tom Engelsman
Jul 12, 2020

The above integrand can be written as 1 + 21 8 ( 1 x 4 1 x + 4 ) 1 + \frac{21}{8} (\frac{1}{x-4} - \frac{1}{x+4}) , which integrates into:

0 1 1 + 21 8 ( 1 x 4 1 x + 4 ) d x = x + 21 8 [ ln ( x 4 ) ln ( x + 4 ) ] 0 1 = 1 + 21 8 l n ( 3 5 ) . \int_{0}^{1} 1 + \frac{21}{8} (\frac{1}{x-4} - \frac{1}{x+4}) dx = x + \frac{21}{8}[\ln(x-4) - \ln(x+4)]|_{0}^{1} = \boxed{1 + \frac{21}{8} \cdot ln( \frac{3}{5} )}.

Chew-Seong Cheong
Jul 14, 2020

I = 0 1 x 2 + 5 x 2 16 d x = 0 1 x 2 16 + 21 x 2 16 d x = 0 1 ( 1 + 21 ( x 4 ) ( x + 4 ) ) d x = 0 1 ( 1 + 21 8 ( 1 x 4 1 x + 4 ) ) d x = x + 21 8 ln x 4 x + 4 0 1 = 1 + 21 8 ( ln 3 5 ln 4 4 ) = 1 + 21 ( ln 3 ln 5 ) 8 0.341 \begin{aligned} I & = \int_0^1 \frac {x^2+5}{x^2-16} dx \\ & = \int_0^1 \frac {x^2-16+21}{x^2-16} dx \\ & = \int_0^1 \left(1 + \frac {21}{(x-4)(x+4)} \right) dx \\ & = \int_0^1 \left(1 + \frac {21}8 \left(\frac 1{x-4} - \frac 1{x+4} \right) \right) dx \\ & = x + \frac {21}8 \ln \left|\frac {x-4}{x+4} \right|\ \bigg|_0^1 \\ & = 1 + \frac {21}8 \left(\ln \frac 35 - \ln \frac 44 \right) \\ & = 1 + \frac {21(\ln 3-\ln 5)}8 \approx \boxed{-0.341} \end{aligned}

Amazing sir thanks

Aly Ahmed - 11 months ago

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You are welcome

Chew-Seong Cheong - 11 months ago

Thanks for the partial fraction details, Chew-Seong! I was too tired to write it out in mine @ Midnite ;)

tom engelsman - 11 months ago

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Sorry, for posting similar solution. I just needed to show things in detail.

Chew-Seong Cheong - 11 months ago

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