Inverse Integrals

Calculus Level 2

Find the shaded area of ± 1 x \pm\ \dfrac{1}{x} for 2 x , y 2 -2 \le x,y\le 2 .


The answer is 9.5452.

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1 solution

Sascha Rankin
Apr 14, 2018

The formula for the area under the inverse function ± 1 x \pm\ \frac{1}{x} with a range and domain constrained by a x , y a -a \leq x,y \leq a can be defined as:

1 4 A r e a = 1 + 1 / a a 1 x d x \frac{1}{4}\ Area = 1 + \int_{1/a}^{a} \frac{1}{x}\ dx

Where the 1 prior to the integral is found by taking the area of the rectangle where f ( x ) = a , f ( a ) = 1 / a , A r e c = 1 f(x)=a,\ f(a)=1/a,\ \therefore A_{rec} = 1

Solving yields:

A 4 = ln x 1 / a a = ln a ln ( 1 / a ) \frac{A}{4}=\ln{x}|_{1/a}^{a}=\ln{a}-\ln{(1/a)}

A r e a = 4 ( 1 + 2 ln a ) Area = 4(1+2\ln{a})

A = 4 ( 1 + 2 ln 2 ) 9.5452 \therefore A = 4(1+2\ln{2}) \approx 9.5452

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