We could write it x sub i minus mu times x sub i minus mu, so we have x sub i times x sub i, that's x sub i squared. Then you have x sub i times mu, times minus mu, and then you have minus u times x sub i. So when you add those two together, you get minus 2 x sub i mu, because you have it twice. x sub i times mu, that's 1 minus x sub i mu. And then you have another one, minus mu x sub i. When you add them together, you get minus 2 x sub i mu. I know it's confusing with me saying sub i and all of that, but it's really no different than when you did a minus b squared, just the variables look a little bit more complicated.