Theory:

Objective:
  
To find a square of the decimal number.
 
We can follow the below steps to find out the square of the decimal numbers.
Step 1: First calculate the square of the given decimal number without the decimal.
 
Step 2: Put the decimal point in the obtained number such that it is twice that of the original number.
 
Note:
 
i) If the original  number contains single decimal, then the square of that number will be double decimal. Numberofdecimalsintheoriginalnumber×2=1×2=2
 
ii) If the original  number contains double decimal, then the square of that number will have four decimal.
 
Numberofdecimalsintheoriginalnumber×2=2×2=4
Find out the square of 7.4.
 
Apply the theory mentioned above.
 
Step 1: Calculate the square of the given decimal number.
 
(742)=74×74=5476.
 
Step 2: Now put the decimal point in the obtained number such that it is twice that of the original number.
 
That is the given number has a single decimal then the answer would be double decimal.
 
7.42=54.76.
 
Therefore the square of a given decimal number is 7.4 \(=\) 54.76.
 
So using the above method, we can easily find the square of decimal numbers.