Answer: option 3
Explanation:
An identity is an equation that is true for all values of the variables. In other words, if an equation is an identity, then it holds true regardless of what values are plugged in for the variables.
Out of the given options, the only equation that is an identity is:
(3) +9= (x+3)
This equation simplifies to:
x + 9 = x + 9
Which is true for all values of x.
Option (1) and (4) are examples of factorization of a quadratic expression and option (2) is an example of a distribution of terms over parentheses, but they are not identities.