# discrete probability density function!

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• Oct 17th 2008, 07:13 AM
sinni8
discrete probability density function!
need help with discrete probability density function!

Find the value of a such that f(x)=a2^-x may be used as a discrete probability density function for X is equal or greater than 0

what i did was i thought since its density function so
it should be 1=a2^-x
really dont know how to do the rest!!
please helP!
• Oct 17th 2008, 08:30 AM
Plato
Solve $\sum\limits_{n = 0}^\infty {\frac{a}{{2^n }}} = 1$ for a.