I think you are confusing "Bernoulli distribution" with "Bernoulli shortcut". If your book says it is using the "Bernoulli shortcut", it must have an explanation of that. Have you tried looking it up in the index?
I know how to find the solution through finding and , but my book gives an alternative solution that I haven't seen before.
Alternative solution:
I know that the variance of the Bernoulli distribution is , but if that's what the book is referring to, what's with the part?
I think you are confusing "Bernoulli distribution" with "Bernoulli shortcut". If your book says it is using the "Bernoulli shortcut", it must have an explanation of that. Have you tried looking it up in the index?
Nevermind, I figured it out. Since Y can only take on two values, you can find the variance the same way it's found in the Bernoulli distribution.