So this is the same thing as the sum from i is equal to 1 to n. Let's see, this we just multiply it out. This is the same thing as x sub i squared minus, this is your little algebra going on here. So when you square it, I mean, we could multiply it out. 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.