# Probability density function

• Oct 8th 2009, 06:06 PM
chengbin
Probability density function
http://i33.tinypic.com/142g900.jpg

How do you get f(x) for XS 26b 2. (1)?
• Oct 8th 2009, 06:11 PM
mr fantastic
Quote:

Originally Posted by chengbin

How do you get f(x) for XS 26b 2. (1)?

Equation of line passing through (3, 0) and (6, k).

Equation of line passing through (6, k) and (9, 0).
• Oct 8th 2009, 06:13 PM
awkward
What is the equation of the line through the points (0,3) and (6,k)?

And what is the equation of the line through the points (6,k) and (0,9)?

Beaten to the punch by Mr. F!
• Oct 9th 2009, 09:41 AM
qpmathelp
What is the equation of the line through the points (3,0) and (6,k)?

note that the point is (3,0 ) and not (0,3)

two point form

(y-y1) / (y2 - y1) =(x-x1) / (x2 - x1)

(y - 0) / (k-0) = (x-3) / (6-3)

simplify and solve for y

y = (k/3) [x-3]

formulae on analytical geometry -----straight lines
• Oct 9th 2009, 10:26 AM
aman_cc
Maybe little off-the-track, but an very easy way is to just equate the area of tri-angle = 1

1/2 x base x height = 1/2 x 6 x k = 1 => k = 1/3
• Oct 9th 2009, 11:42 AM
chengbin
I have to set up an integral (talk about practice for calculus)

I feel stupid that I didn't see that I find the equation of the line for it.
• Oct 9th 2009, 12:03 PM
CaptainBlack
Quote:

Originally Posted by chengbin
I have to set up an integral (talk about practice for calculus)

I feel stupid that I didn't see that I find the equation of the line for it.

No you don't (ignore the given solution), the pdf is a triangle the area under the curve has to be 1 for it to be a pdf, the base is 6, the height k, so the area is 3k=1, so k=1/3.

The given solution has been done by a moron, this question is to test your understanding of pdf's not of algebra and calculus.

CB
• Oct 9th 2009, 07:31 PM
mr fantastic
Quote:

Originally Posted by CaptainBlack
[snip]
The given solution has been done by a moron, this question is to test your understanding of pdf's not of algebra and calculus.

CB