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Find CDF when knowing PDF, also find E[X]


Finding CDF for PDFFind constant $c$ for piecewise continuous random variable pdfGiven a CDF find the PDFHow to find the CDF and PDFFind the CDF from the PDF.Finding probability density function for $Z$ which is a function of $X$ and $Y$Set $Z=X+Y$ and calculate the density function $f_Z$ for Z. Given solution doesn't match mine. (Continuous R.V)Find cdf given pdf.Find the cumulative probability function given a probability density functionProbability of one random variable less than two otherSpiral path quasi-CDF sampling approach question













0












$begingroup$


i lose my login information and have to make new account
i apologies for my poor english



i am given a problem as such:



$$ f(x) = begincases
c(1-x^2), & -1<x<0, \ c/x^2, & 1<x<2, \ 0, & textotherwise.
endcases$$



first step is to find c



I calculate c = 6 by following:



$$ int^0_-1 c(1-x^2) , dx + int^2_1 fraccx^2 , dx = 1 $$



is this correct?



2 more part to the problem which trouble me



find CDF $$ F(X) = ? $$



find E(X)
$$ E(x) = int_-infty^inftyxf(x)dx $$



i am trouble by the f(x) not being continue from 0, 1
this is a new problem sort to me



to the one who helps me i am very thankful










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    No, $displaystyle c=frac67$
    $endgroup$
    – Extremal
    Dec 7 '14 at 17:32
















0












$begingroup$


i lose my login information and have to make new account
i apologies for my poor english



i am given a problem as such:



$$ f(x) = begincases
c(1-x^2), & -1<x<0, \ c/x^2, & 1<x<2, \ 0, & textotherwise.
endcases$$



first step is to find c



I calculate c = 6 by following:



$$ int^0_-1 c(1-x^2) , dx + int^2_1 fraccx^2 , dx = 1 $$



is this correct?



2 more part to the problem which trouble me



find CDF $$ F(X) = ? $$



find E(X)
$$ E(x) = int_-infty^inftyxf(x)dx $$



i am trouble by the f(x) not being continue from 0, 1
this is a new problem sort to me



to the one who helps me i am very thankful










share|cite|improve this question











$endgroup$







  • 1




    $begingroup$
    No, $displaystyle c=frac67$
    $endgroup$
    – Extremal
    Dec 7 '14 at 17:32














0












0








0





$begingroup$


i lose my login information and have to make new account
i apologies for my poor english



i am given a problem as such:



$$ f(x) = begincases
c(1-x^2), & -1<x<0, \ c/x^2, & 1<x<2, \ 0, & textotherwise.
endcases$$



first step is to find c



I calculate c = 6 by following:



$$ int^0_-1 c(1-x^2) , dx + int^2_1 fraccx^2 , dx = 1 $$



is this correct?



2 more part to the problem which trouble me



find CDF $$ F(X) = ? $$



find E(X)
$$ E(x) = int_-infty^inftyxf(x)dx $$



i am trouble by the f(x) not being continue from 0, 1
this is a new problem sort to me



to the one who helps me i am very thankful










share|cite|improve this question











$endgroup$




i lose my login information and have to make new account
i apologies for my poor english



i am given a problem as such:



$$ f(x) = begincases
c(1-x^2), & -1<x<0, \ c/x^2, & 1<x<2, \ 0, & textotherwise.
endcases$$



first step is to find c



I calculate c = 6 by following:



$$ int^0_-1 c(1-x^2) , dx + int^2_1 fraccx^2 , dx = 1 $$



is this correct?



2 more part to the problem which trouble me



find CDF $$ F(X) = ? $$



find E(X)
$$ E(x) = int_-infty^inftyxf(x)dx $$



i am trouble by the f(x) not being continue from 0, 1
this is a new problem sort to me



to the one who helps me i am very thankful







probability probability-distributions






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 7 '14 at 18:13









mathisfun

18112




18112










asked Dec 7 '14 at 17:26









chinpichinpi

1




1







  • 1




    $begingroup$
    No, $displaystyle c=frac67$
    $endgroup$
    – Extremal
    Dec 7 '14 at 17:32













  • 1




    $begingroup$
    No, $displaystyle c=frac67$
    $endgroup$
    – Extremal
    Dec 7 '14 at 17:32








1




1




$begingroup$
No, $displaystyle c=frac67$
$endgroup$
– Extremal
Dec 7 '14 at 17:32





$begingroup$
No, $displaystyle c=frac67$
$endgroup$
– Extremal
Dec 7 '14 at 17:32











1 Answer
1






active

oldest

votes


















0












$begingroup$

You calculated $c$ wrong. It should be $c = frac67$ and then according to:
Finding CDF for PDF
You will get the following CDF:
beginequation
F(x) =
begincases
0, text if x<-1 \
frac17 left(4+6t-2t^3 right), text if x in [-1,0]\
frac47, text if x in [0,1] \
frac47+frac67 left(1-frac1t right) text if x in [1,2] \
1, text if x>2
endcases
endequation
For expectation, you should split your integral in the same way.
$$mathrmE, [X] = int_-1^0 frac67 x (1-x^2) , mathrmd , x + int_1^2 frac67x , mathrmd x = frac67 ln2 - frac314$$
I hope I didn't do a mistake in expectation.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    how can this be? this gives F(0.999) = 1.14 which > 1?
    $endgroup$
    – chinpi
    Dec 7 '14 at 18:35










  • $begingroup$
    @chinpi sure, made some correction
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:00






  • 1




    $begingroup$
    $E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
    $endgroup$
    – Math-fun
    Dec 7 '14 at 19:05











  • $begingroup$
    @Mehdi sure, let me correct this
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:06










  • $begingroup$
    this is now correct, and i am happy i thank you kindly
    $endgroup$
    – chinpi
    Dec 7 '14 at 19:11










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1 Answer
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active

oldest

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









0












$begingroup$

You calculated $c$ wrong. It should be $c = frac67$ and then according to:
Finding CDF for PDF
You will get the following CDF:
beginequation
F(x) =
begincases
0, text if x<-1 \
frac17 left(4+6t-2t^3 right), text if x in [-1,0]\
frac47, text if x in [0,1] \
frac47+frac67 left(1-frac1t right) text if x in [1,2] \
1, text if x>2
endcases
endequation
For expectation, you should split your integral in the same way.
$$mathrmE, [X] = int_-1^0 frac67 x (1-x^2) , mathrmd , x + int_1^2 frac67x , mathrmd x = frac67 ln2 - frac314$$
I hope I didn't do a mistake in expectation.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    how can this be? this gives F(0.999) = 1.14 which > 1?
    $endgroup$
    – chinpi
    Dec 7 '14 at 18:35










  • $begingroup$
    @chinpi sure, made some correction
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:00






  • 1




    $begingroup$
    $E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
    $endgroup$
    – Math-fun
    Dec 7 '14 at 19:05











  • $begingroup$
    @Mehdi sure, let me correct this
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:06










  • $begingroup$
    this is now correct, and i am happy i thank you kindly
    $endgroup$
    – chinpi
    Dec 7 '14 at 19:11















0












$begingroup$

You calculated $c$ wrong. It should be $c = frac67$ and then according to:
Finding CDF for PDF
You will get the following CDF:
beginequation
F(x) =
begincases
0, text if x<-1 \
frac17 left(4+6t-2t^3 right), text if x in [-1,0]\
frac47, text if x in [0,1] \
frac47+frac67 left(1-frac1t right) text if x in [1,2] \
1, text if x>2
endcases
endequation
For expectation, you should split your integral in the same way.
$$mathrmE, [X] = int_-1^0 frac67 x (1-x^2) , mathrmd , x + int_1^2 frac67x , mathrmd x = frac67 ln2 - frac314$$
I hope I didn't do a mistake in expectation.






share|cite|improve this answer











$endgroup$












  • $begingroup$
    how can this be? this gives F(0.999) = 1.14 which > 1?
    $endgroup$
    – chinpi
    Dec 7 '14 at 18:35










  • $begingroup$
    @chinpi sure, made some correction
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:00






  • 1




    $begingroup$
    $E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
    $endgroup$
    – Math-fun
    Dec 7 '14 at 19:05











  • $begingroup$
    @Mehdi sure, let me correct this
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:06










  • $begingroup$
    this is now correct, and i am happy i thank you kindly
    $endgroup$
    – chinpi
    Dec 7 '14 at 19:11













0












0








0





$begingroup$

You calculated $c$ wrong. It should be $c = frac67$ and then according to:
Finding CDF for PDF
You will get the following CDF:
beginequation
F(x) =
begincases
0, text if x<-1 \
frac17 left(4+6t-2t^3 right), text if x in [-1,0]\
frac47, text if x in [0,1] \
frac47+frac67 left(1-frac1t right) text if x in [1,2] \
1, text if x>2
endcases
endequation
For expectation, you should split your integral in the same way.
$$mathrmE, [X] = int_-1^0 frac67 x (1-x^2) , mathrmd , x + int_1^2 frac67x , mathrmd x = frac67 ln2 - frac314$$
I hope I didn't do a mistake in expectation.






share|cite|improve this answer











$endgroup$



You calculated $c$ wrong. It should be $c = frac67$ and then according to:
Finding CDF for PDF
You will get the following CDF:
beginequation
F(x) =
begincases
0, text if x<-1 \
frac17 left(4+6t-2t^3 right), text if x in [-1,0]\
frac47, text if x in [0,1] \
frac47+frac67 left(1-frac1t right) text if x in [1,2] \
1, text if x>2
endcases
endequation
For expectation, you should split your integral in the same way.
$$mathrmE, [X] = int_-1^0 frac67 x (1-x^2) , mathrmd , x + int_1^2 frac67x , mathrmd x = frac67 ln2 - frac314$$
I hope I didn't do a mistake in expectation.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Apr 13 '17 at 12:20









Community

1




1










answered Dec 7 '14 at 17:56









mathisfunmathisfun

18112




18112











  • $begingroup$
    how can this be? this gives F(0.999) = 1.14 which > 1?
    $endgroup$
    – chinpi
    Dec 7 '14 at 18:35










  • $begingroup$
    @chinpi sure, made some correction
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:00






  • 1




    $begingroup$
    $E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
    $endgroup$
    – Math-fun
    Dec 7 '14 at 19:05











  • $begingroup$
    @Mehdi sure, let me correct this
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:06










  • $begingroup$
    this is now correct, and i am happy i thank you kindly
    $endgroup$
    – chinpi
    Dec 7 '14 at 19:11
















  • $begingroup$
    how can this be? this gives F(0.999) = 1.14 which > 1?
    $endgroup$
    – chinpi
    Dec 7 '14 at 18:35










  • $begingroup$
    @chinpi sure, made some correction
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:00






  • 1




    $begingroup$
    $E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
    $endgroup$
    – Math-fun
    Dec 7 '14 at 19:05











  • $begingroup$
    @Mehdi sure, let me correct this
    $endgroup$
    – mathisfun
    Dec 7 '14 at 19:06










  • $begingroup$
    this is now correct, and i am happy i thank you kindly
    $endgroup$
    – chinpi
    Dec 7 '14 at 19:11















$begingroup$
how can this be? this gives F(0.999) = 1.14 which > 1?
$endgroup$
– chinpi
Dec 7 '14 at 18:35




$begingroup$
how can this be? this gives F(0.999) = 1.14 which > 1?
$endgroup$
– chinpi
Dec 7 '14 at 18:35












$begingroup$
@chinpi sure, made some correction
$endgroup$
– mathisfun
Dec 7 '14 at 19:00




$begingroup$
@chinpi sure, made some correction
$endgroup$
– mathisfun
Dec 7 '14 at 19:00




1




1




$begingroup$
$E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
$endgroup$
– Math-fun
Dec 7 '14 at 19:05





$begingroup$
$E[x]$ is wrong. Please note that the upper bound on the first integral to calculate $E[x]$ should be $0$ instead of $1$.
$endgroup$
– Math-fun
Dec 7 '14 at 19:05













$begingroup$
@Mehdi sure, let me correct this
$endgroup$
– mathisfun
Dec 7 '14 at 19:06




$begingroup$
@Mehdi sure, let me correct this
$endgroup$
– mathisfun
Dec 7 '14 at 19:06












$begingroup$
this is now correct, and i am happy i thank you kindly
$endgroup$
– chinpi
Dec 7 '14 at 19:11




$begingroup$
this is now correct, and i am happy i thank you kindly
$endgroup$
– chinpi
Dec 7 '14 at 19:11

















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