# Thread: Given a PDF function, find the CDF! exam tomorrow! please give descriptive answers!

1. ## Given a PDF function, find the CDF! exam tomorrow! please give descriptive answers!

Probability density function (PDF) is given by the expression fx(x)=ae-b|x|. Here X is a random variable whose values lie in the range x=-infinity to +infinity. Determine the following
a) The relationship in between a & b.
b) Cumulative density function (CDF)
c) The probability that outcome lies between 1 & 2.

2. ## Re: Given a PDF function, find the CDF! exam tomorrow! please give descriptive answer

1)for the relationship between a&b, you need to integrate the density from -infinity to +infinity and set that equal to 1. then using that answer, you can establish a relationship between a&b that ensure that fx(x) is a valid density.
2) for the cdf, you just integrate this $\displaystyle \int_{-\infty}^{x}ae^{-b|u|}du$
3) for this, you should use $\displaystyle \int_{1}^{2}ae^{-b|x|}dx$

being able to do this question requires understanding of basic integration