(i) The square root of 402 can be calculated by long division method as follows:

The remainder is 2

This represents that the square of 20 is less than 402 by 2.

Hence, a perfect square will be obtained by subtracting 2 from the given number 402

Therefore, required perfect square = 402 - 2

= 400

= 20

(ii) The square root of 1989 can be calculated by long division method as follows:

The remainder is 53

This represents that the square of 44 is less than 1989 by 53

Hence, a perfect square will be obtained by subtracting 53 from the given number 1989.

Therefore, required perfect square = 1989 - 53

= 1936

= 44

(iii) The square root of 3250 can be calculated by long division method as follows:

The remainder is 1

This represents that the square of 57 is less than 3250 by 1

Hence, a perfect square can be obtained by subtracting 1 from the given number 3250.

Therefore, required perfect square = 3250 - 1

= 3249

= 57

(iv) The square root of 825can be calculated by long division method as follows:

The remainder is 41

This represents that the square of 28 is less than 825 by 41

Hence, a perfect square can be calculated by subtracting 41 from the given number 825

Therefore, required perfect square = 825 – 41

= 784

= 28

(v) The square root of 4000 can be calculated by long division method as follows:

The remainder is 31

This represents that the square of 63 is less than 4000 by 31

Hence, a perfect square can be calculated by subtracting 31 from the given number 4000

Therefore, required perfect square = 4000 – 31

= 3969

= 63