X is that far from mu. The population variances are equal. Samples are randomly selected. This number is derived from the theoretical t-distribution. Use Table C in the back of the book.
Power is the probability of correctly rejecting the null.
No expected effect, that is no differences between the two sample means. What you are testing Hypothesize that there IS a difference between the two sample means and that difference is more than would be expected by chance alone Can be unidirectional or bi-directional. Only use unidirectional if you have a very good reason to predict that the direction of the difference is one way or another. This number is derived from the theoretical t-distribution.