# Math Help - Cumulative distribution function

1. ## Cumulative distribution function

We have cumulative distribution function Fx.

Fx = 1/1000x - 1/4

How do we get probability density function (gx) from Fx?

If we have gx, to get Fx, we need to integrate from 0 to x. Am I right?

So to get gx from Fx, we need to find the derivative, because it's an opposite operation from integration.

2. Originally Posted by Nforce
We have cumulative distribution function Fx.

Fx = 1/1000x - 1/4

How do we get probability density function (gx) from Fx?

If we have gx, to get Fx, we need to integrate from 0 to x. Am I right?

So to get gx from Fx, we need to find the derivative, because it's an opposite operation from integration.
g(x) = dF/dx.

By the way, your definition of F(x) is very incomplete, you should have included the values of x for which the given rule applies. As it happens, I doubt very much that what you posted defines a valid cdf.

3. yes i have forgot; the interval is [250,1250]

I don't completely understand this:

g(x) = dF/dx.

What is dF in here? Do you mean the derivative? Can you solve for example above.

4. Originally Posted by Nforce
yes i have forgot; the interval is [250,1250]

I don't completely understand this:

g(x) = dF/dx.

What is dF in here? Do you mean the derivative? Can you solve for example above.
Of course it's the derivative. What else could it possibly be?

I have no intention of solving it. Surely you know how to find the derivative of a function.

5. ok, thank you.