Look for the pattern of square numbers.
What will be the multiplication of a negative number by itself?
Just look at the digit at unit place and try to find the square of it.
How to find the area of a square?
Just recall your times table.
Square of an odd number is an odd number.
Just double the number of zeros.
Think of the square number of 20 and 21.
Look for the pattern of square numbers.
How to find the area of a square?