Consisting of 16 basic aphorisms or Sutras, Vedic Mathematics is a system of Maths which prevailed in ancient India. Composed by Bharati Krishna Thirtha, these 16 sutras help one to do faster maths.
The first aphorism is this
“Whatever the extent of its deficiency, lessen it still further to that very extent; and also set up the square (of that deficiency)”
When computing the square of 9, as the nearest power of 10 is 9, let us take 10 as our base. As 9 is 1 less than 10, we can decrease it by the deficiency = 9-1 =8. This is the leftmost digit
On the right hand put deficiency^2, which is 1^2.
Hence the square of nine is 81.
For numbers above 10, instead of looking at the deficit we look at the surplus.
For example:
11^2 = (11+1)*10+1^2 = 121
12^2 = (12+2)*10+2^2 = 144
14^2 = ( 14+4)*10+4^2 = 196
25^2 = ((25+5)*2)*10+5^2 = 625
35^2= ((35+5)*3)*10+5^2 = 1225