Multiplication of two numbers that differ by 2
Note :This trick only works if you know the squares of
numbers.
When two numbers differ by 2,
their product is always the square of the number in between these numbers minus
1.
12 x 14 = (13 x 13) - 1 = 169 - 1 = 168
18 x 20 = (19 x 19) - 1 = 361 - 1 = 360
25 x 27 = (26 x26) - 1 = 676 - 1 = 675
13 x 15 = (14 x 14) - 1 = 196 - 1 = 195
13 x 15 = (14 x 14) - 1 = 196 - 1 = 195
15 x 17 = (16 x 16) - 1 = 256 - 1 = 255
16 x 18 = (17 x 17) - 1 = 289 - 1 = 288