# Math Help - Finding the expectation of X_2

1. ## Finding the expectation of X_2

Given $(X_1,X_2,...,X_{k-1})$ has a Dirichlet distribution wiht parameters $(\alpha_1,...,\alpha_k)$

With $\alpha_{i+}=\alpha_i+...+\alpha_k$

I want to find $E[X_2]$

I know that $E[X_1]=\frac{\alpha_1}{\alpha_{1+}}$ since $X_1 \sim Beta(\alpha,\alpha_{2+})$

and

$(\frac{X_2}{1-X_1}|X_1) \sim Beta(\alpha_2,\alpha_{3+})$

2. ## Re: Finding the expectation of X_2

If you want to use latex you have to use [ tex ] ... [ /tex ] in stead of [ math ] ... [ /math ]