Let us assume decimal number be ‘a’.
We know that, a × a = a2
So,
a × a = 51.84
a2 = 51.84
a = √51.84
The required number is found out by using long division method.
Then,
a = √51.84
a = 7.2
∴7.2 is the decimal number is multiplied by itself and its product is 51.84.