in this exercise you will prove that the sum of a collection of independent chi-squared random variables also has a chi-squared distribution. Recall that chi-squared was a special case of the gamma distribution with β = 2 and α = γ/2. Let X1, . . . , Xn be independent chi-squared random variables with γ1, γ2, γ3, . . . , γn degrees of freedom, respectively. Let Y = X1 + X2 + X3 + · · · + Xn. Show that Y is a chi-squared random variable with γ degrees of freedom where γ = Pn i=1 γi.