Answer :
We are given the expression:
$$12x^2 + 9x^2.$$
Since both terms have the same variable part, $x^2$, we can combine them by adding their coefficients.
Step 1: Write the coefficients of the like terms.
- The coefficient of the first term is $12$.
- The coefficient of the second term is $9$.
Step 2: Add the coefficients:
$$12 + 9 = 21.$$
Step 3: Attach the common variable part $x^2$ to the sum of the coefficients to get:
$$21x^2.$$
Thus, the sum is:
$$21x^2.$$
The correct answer is A. $21x^2$.
$$12x^2 + 9x^2.$$
Since both terms have the same variable part, $x^2$, we can combine them by adding their coefficients.
Step 1: Write the coefficients of the like terms.
- The coefficient of the first term is $12$.
- The coefficient of the second term is $9$.
Step 2: Add the coefficients:
$$12 + 9 = 21.$$
Step 3: Attach the common variable part $x^2$ to the sum of the coefficients to get:
$$21x^2.$$
Thus, the sum is:
$$21x^2.$$
The correct answer is A. $21x^2$.
