(x-1)*(x+1) = x2 - x + x - 1 = x2 - 1
So, when x = 30,
29*31 = 30*30 - 1
Or, since 30*30 = 900, 29*31 = 900-1 = 899
One example is 1 + 899.
899
900
It is: 899+1 = 900
1-900 = -899
900
100 centimeters equals a meter. Multiply 9 times 100. 900 centimeters equals 9 meters.
To get the next number after any number, just add 1.
One less than 900 is 899.
The number just before 900 is 899.
The number is still 899, but it has been rounded to 1,000 .
30 x 30 = 900