When i was in high school, i figured out how to square a number in an unconventional way. My trignometry teacher was impressed:
Lets square 47: 47 x 47 = 2209. Well, we all know how to manually multiply. But what i figured out was an alternative formula to figure out the answer:
the first digit is X and the second digit is Y. thus, in this example, X=4 and Y=7.
take X and multiple it by X +1: 4 x (4+1) = 4 x 5 = 20.
take Y and multiple it by itself: 7 x 7 = 49
slide the two values together: 2049
Then adjust the value based on a constant (k) that i had to work out but is sound. the constant is based on the value of y and then multiple by x. this was actually the trickiest part to figure out.
y=1, K=-80
y=2, K=-60
y=3, K=-40
y=4, K=-20
y=5, K=0,
y=6, k=20
y=7, k=40
y=8, k=60
y=9, k=80.
2049 + (K x X)
2049 + (40 x 4)
2049 +160=2209
However, the equation broke down when y = 1, 2, or 3. The only way to resolve this problem was to create another constant, C. This constant is 10 when y=1,2, or 3 and the constant is 1 when y=4,5,6,7,8,9. Putting everything together, the final formula to square a number is:
C[(X)(X+1)] slide (Y)(Y) + X(K)
Let us square 81. X=8, Y=1, C=10, K=-80
10[(8)(9)] slide (1)(1) +8(-80)
10(72) slide 1 + (-640)
720 slide 1 -640
7201-640
6561
Kind of phucked-up actually.