[bigboy1111452]

Well they give the mean as 2 and the variance as 9.

I am meant to find the answer of E[(y-1)(y+1)]
how do i do it?

[Shaare]

Try expanding the bracket inside and then think about how you can use what has been given to you to work out the answer.

[aznkid66]

If you're still having trouble, here are more hints:

Spoiler:

Show

Mean of X = E[X]
Variance of X = E[X^2]-E[X]^2
Mean of X+c = E[X+c] = E[X]+c

[bigboy1111452]

Still can't get it

[natninja]

(Original post by bigboy1111452)
Well they give the mean as 2 and the variance as 9.

I am meant to find the answer of E[(y-1)(y+1)]
how do i do it?

the answer is 'y'

edit: ignore that wasn't thinking that 'y' is the distribution

[Shaare]

E[(y+1)(y-1)] = E(Y²-1) = E(Y²)-1

Now, what is E(Y²)? Think about the relationship between E(Y²), E(Y) and Var(Y).

[aznkid66]

More helpful versions of the equations:

Spoiler:

Show

Mean of X = E[X]
Mean of Y = E[Y] = 2

Variance of X = E[X²]-E[X]²
Variance of Y = E[Y²]-E[Y]²=E[Y²]-2² = 9
Therefore: Mean of Y² = ...

E[X+c] = E[X] + c
E[(Y-1)(Y+1)] = E[Y²-1] = E[Y²]-1