Thread: Variance from MGF

Could you please help me with the following, I know you have to differentiate but I am not saure if I am doing it right, could you please show intermediate steps.

If X has the moment generating function given by

MX(t) = cos(7.21t)+ 7.21t* sin(24.85t)

what is the variance of X ?

Originally Posted by javs156

Could you please help me with the following, I know you have to differentiate but I am not saure if I am doing it right, could you please show intermediate steps.

If X has the moment generating function given by

MX(t) = cos(7.21t)+ 7.21t* sin(24.85t)

what is the variance of X ?

You should know that:

.

.

Therefore .

If you show your working it will be much easier to check if you're "doing it right".