# Thread: basic problem computing pdf

1. ## basic problem computing pdf

If I have a pdf, say X~Uniform[-3,3] and Y= -X, would the pdf of Y be 1/6 [-3,3] ? How would I get the pdf using P(-X < - y) = P(X > y) = 1 - P( X < y) = 1- integral 1/6 from -3,3 so differentiating to get pdf we get -1/6 for [-3,3] but the pdf is negative so I assume my assumption Y is 1/6 is right. Where did I make my mistake?

2. ## Re: basic problem computing pdf

Ok suppose you are first computing the CDF:

For ,

(Note that so the following integral hold)

Therefore by differentiation you obtain the desired answer.

Outside this range the CDF of is constant (0 or 1) so is the support of

3. ## The Following User Says Thank You to BGM For This Useful Post:

stephanie (11-29-2013)

4. ## Re: basic problem computing pdf

Thank you this really helped me

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