Squaring a 2-digit number ending in 2

Steps
take a 2-digit number ending in 2.
the last digit will be ___4.
multiply the first digit by 4: the second number will be the next to the last digit: __X4.
square the first digit and add the number carried from the previous step: XX__.

Example
if the number is 52, the last digit is ___4.
4 x 5 = 20 : __04.
5 x 5 = 25, 25 + 2 = 27 (add carry): 2704.
so 52 x 52 = 2704.