SQUARING a 2-DIGIT NUMBER ENDING IN 1

STEPS

take a-2 digit number ending in 1.
substract 1 from the number.
square the difference.
add the difference twice to its square.
add 1.

EXAMPLE

If the number is 41, substract 1 : 41-1=40.
40 x 40 = 1600 ( square the difference ).
1600 + 40 + 40 =1680 ( add the difference twice to its square ).
1680 + 1 = 1681 ( add 1 ).
so 41 x 41 = 1681