What is the formula for the variance of 3 dependent variables?

For 2 dependent variables, the formula is

Var(X)+Var(Y)+2*Cov(X,Y)

What is Var(X+Y+Z) if the variables are dependent? Please do not give me the general formula for n number of variables. I've seen it but I don't understand it. If I see an example with 3 variables then I think I can figure it out. Thanks.

For 2 dependent variables, the formula is

Var(X)+Var(Y)+2*Cov(X,Y)

What is Var(X+Y+Z) if the variables are dependent? Please do not give me the general formula for n number of variables. I've seen it but I don't understand it. If I see an example with 3 variables then I think I can figure it out. Thanks.

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