I'd like to know how do we calculate manually this following operation :

[(1-2.8)^2*1+(2-2.8)^2*3+(3-2.8)^2*2+(4-2.8)^2*2+(5-2.8)^2*1]/10=?

More specifically I'm interested in knowing how do we break down the numbers in brackets that are

**to the power of two**such as

**(1-2.8)^2***1+

**(2-2.8)^2***3 etc, because no matter in what way I try to do it by myself without the help of a calculator the results do not coincide unfortunately.

Your help would be greatly appreciated!