MATLAB: An Introduction with Applications
MATLAB: An Introduction with Applications
6th Edition
ISBN: 9781119256830
Author: Amos Gilat
Publisher: John Wiley & Sons Inc
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Question

f (x) = c/x3/4 for 0 < x < 1; Find the constant c so that f (x) is a
pdf of some random variable X, and then find the cdf, F (x) = P(X ≤ x). Sketch graphs
of the pdf f (x) and the cdf F (x), and find the mean μ and variance σ2.

Expert Solution
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Step 1: we will define the f(x) then find out the constant value c

Given

f left parenthesis x right parenthesis equals c over x to the power of bevelled 3 over 4 end exponent space f o r space 0 less than x less than 1 space

we find the constant c such that f left parenthesis x right parenthesis is a pdf of some random variable X

we need to ensure that the integral of f left parenthesis x right parenthesis over its entire domain equals to 1:

integral subscript 0 superscript 1 f left parenthesis x right parenthesis d x equals 1
W e space h a v e space g i v e n space f left parenthesis x right parenthesis equals c over x to the power of bevelled 3 over 4 end exponent space f o r space 0 less than x less than 1
integral subscript 0 superscript 1 c over x to the power of bevelled 3 over 4 end exponent d x equals 1
c open parentheses fraction numerator x to the power of negative 3 over 4 plus 1 end exponent over denominator negative 3 over 4 plus 1 end fraction close parentheses subscript 0 superscript 1 equals 1
c open parentheses fraction numerator x to the power of 1 fourth end exponent over denominator 1 fourth end fraction close parentheses subscript 0 superscript 1 equals 1
c open parentheses fraction numerator 1 to the power of 1 fourth end exponent minus 0 to the power of 1 fourth end exponent over denominator 1 fourth end fraction close parentheses equals 1
c equals 1 fourth

the value  bold italic c bold equals bold 1 over bold 4

Hence the pdf of X is,

f left parenthesis x right parenthesis equals fraction numerator 1 over denominator 4 x to the power of bevelled 3 over 4 end exponent end fraction space space f o r space space 0 less than x less than 1

Now we will find the cdf of X

F left parenthesis x right parenthesis equals P left parenthesis X less or equal than x right parenthesis
space space space space space space space space equals integral subscript 0 superscript x f left parenthesis t right parenthesis d t
space space space space space space space space equals integral subscript 0 superscript x fraction numerator 1 over denominator 4 t to the power of bevelled 3 over 4 end exponent end fraction d t
space space space space space space space space equals 1 fourth open parentheses t to the power of negative 3 over 4 plus 1 end exponent over blank to the power of negative 3 over 4 plus 1 end exponent close parentheses subscript 0 superscript x
space space space space space space space space equals 1 fourth open parentheses t to the power of 1 fourth end exponent over blank to the power of 1 fourth end exponent close parentheses subscript 0 superscript x
space space space space space space space space equals 1 fourth open parentheses fraction numerator x to the power of 1 fourth end exponent minus 0 to the power of 1 fourth end exponent over denominator blank to the power of 1 fourth end exponent end fraction close parentheses
F left parenthesis x right parenthesis equals x to the power of bevelled 1 fourth end exponent

Hence the cdf of X is,

F left parenthesis x right parenthesis equals x to the power of bevelled 1 fourth end exponent space space f o r space 0 less than x less than 1

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