# Thread: random variables and variance

1. ## random variables and variance

if we let X be a (continous or discrete) random variable with range
Rx[-a,a]
how can we find Var(X) which is less or equal than a^2??

2. Originally Posted by xixihaha
if we let X be a (continous or discrete) random variable with range
Rx[-a,a]
how can we find Var(X) which is less or equal than a^2??
Please post the entire question, not just your version of it.

$Var(X) = E(X^2) - [E(X)]^2$.

3. that is the entire question.
here is the exactly the question from my sheet:

Let X be a (discrete or continuous) random variable with range Rx[-a,a]. Show that Var(X) =< a^2.