Is This Covariance Calculation Correct?

[jasper90]

I think this is right, just want to double check.

Cov(Y1+Y2, Ʃ n i=2 Yi)= Cov(Y1, Ʃ n i=2) + Cov(Y2, Ʃ n i=2 Yi) = 0 + Var(Y2) = σ^2

is this right?

 

[mathman]

I think this is right, just want to double check.

Cov(Y1+Y2, Ʃ n i=2 Yi)= Cov(Y1, Ʃ n i=2) + Cov(Y2, Ʃ n i=2 Yi) = 0 + Var(Y2) = σ^2

is this right?

Your expressions are confusing. Also you should define Y1 and Y2 and their relationship (if any).
Ʃ n i=2 Yi, Ʃ n i=2 ?