The expression (21.98×21.98+21.98x+0.04×0.04) will be a perfect square if x = ?

Correct option is C

Given: 

 $$(21.98×21.98+21.98x+0.04×0.04)$$​

Formula Used:

$$(a+b)^2 = a^2 + b^2 + 2ab$$ 

​Solution:  

For the given expression to be a perfect square we must have 

​$$21.98×x=2×21.98×0.04\\x=0.08$$​​