1. If we know the square of one number and we don't know the other which is consecutive to number then we can find by adding the both numbers and square of first number.
example: 13square = 169
14square = ?
14square = 13+14+169 = 196
2. if we multiply 2 or 3 or more nines into nine then we have to take out one nine(not subtracting) and add at starting 8 and ending 1.
example: 9999999*9 = ?
9999999 = 999999
999999 = 89999991
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