I have this problem in a book and I've did good through the entire problem until I had to calculate current gain. I've been stuck for the past 30 minutes. The formula I get is different from the one in the book and I'm wondering why. This is probably some simple mathematical thing and I'll probably end up embarrassing myself but I just don't know why I get different current gain. I can't continue if I don't understand this.
What I get is that the second term in current gain (circled red on the picture) is reverse, that is numerator and denominator are reverse. I just need an explanation for that term in the book.