Methods: First, consider this number as the sum (or difference) of multiples of 5 and numbers less than 5, and then add (or subtract) twice the product of these two numbers and the sum of squares of these two numbers.

2. Find the square of any two-digit number

Method: multiply the difference by the sum of the complement of this number plus its single digits, and then add the square of this complement by this product.

Find the square of 1000.

Method: Write the sum of this number plus 2 digits, then write a 0, and finally write the square of the single digit (if the square of the single digit is less than 10, add a 0 before it).

4. Square 990.

Method: Write down the difference of 1000 minus twice the complement of this number, then write a 0, and finally write down the square of the complement (if the square of the complement is less than 10, add a 0 before it).

5. Find the square of the number whose last two digits are 25.

Methods: Multiply the number before the ten digits and then add the number of five, and add 625 after the product.

Extended data:

The square story about.

Legend has it that a foreign minister in India played chess with the king. The king lost and promised to meet his demand: put the rice on the chessboard. Put 1 capsule in the first box, 2 capsules in the second box, then 4 capsules, 8 capsules, 16 capsules ... until 64 capsules are put in. The king smiled and thought that he was stupid and that it was only a little bit of rice.

According to the minister's request, it takes 1 grain to fill 64 squares. This number is1844674073709551615, which is a 20-digit number. Not to mention emptying the treasury, even rice in India and even the whole world can't meet the requirements of this minister!