Intersection of Set theory & Integral Calculus

Calculus Level 3

p = 1 ln 6 5 10 x 2 3 x 4 , d x p = \frac{1}{\ln6} \int_5^\infty \frac{10}{x^2 - 3x - 4} , \, dx

How many sets lie in the power set of set S S if S = { n : n < p } S = \{n:|n|<p\} where n ϵ Z n\ \epsilon\ \mathbb{Z} ?


The answer is 8.

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1 solution

Tom Engelsman
Apr 23, 2021

The above improper integral computes to:

1 ln 6 5 2 x 4 2 x + 1 d x = 1 ln 6 2 [ ln ( x 4 ) ln ( x + 1 ) ] = 2 ln 6 ln ( x 4 x + 1 ) 5 = 2 ln 6 ln ( 1 1 / 6 ) = 2 ln 6 ln 6 = 2. \Large \frac{1}{\ln 6} \cdot \int_{5}^{\infty} \frac{2}{x-4} - \frac{2}{x+1} dx = \frac{1}{\ln 6} \cdot 2[\ln (x-4) - \ln (x+1)] = \frac{2}{\ln 6} \cdot \ln(\frac{x-4}{x+1}) |_{5}^{\infty} = \frac{2}{\ln 6} \cdot \ln(\frac{1}{1/6}) = \frac{2}{\ln 6} \cdot \ln 6 = 2.

If S = 0 , ± 1 S = 0, \pm 1 , then the corresponding power set equals:

( ) ; ( 0 ) ; ( 1 ) ; ( 1 ) ; ( 1 , 0 ) ; ( 0 , 1 ) ; ( 1 , 1 ) ; ( 1 , 0 , 1 ) (\emptyset); (0); (1); (-1); (-1,0); (0,1); (-1,1); (-1, 0,1)

which contains 8 \boxed{8} members.

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