Add 3√21 + 7√21.

3√21 + 7√21 can be simplified by combining like terms since both terms have the same radical.

3√21 + 7√21 = (3 + 7)√21 = 10√21

To add these two terms:

Step 1: Ensure that both terms have the same radical (in this case, √21).
Step 2: Add the coefficients of the like terms.

In this case, both terms have the same radical (√21), so we can add their coefficients.

Coefficient of the first term is 3, and coefficient of the second term is 7.

Adding the coefficients, we get:

3 + 7 = 10

Therefore, the final answer is 10√21.

To add 3√21 and 7√21, you can combine like terms by adding the coefficients. Since both terms have the same radical (√21), you can simply add the coefficients of the radicals.

So, 3√21 + 7√21 = (3 + 7)√21 = 10√21.

Therefore, the sum of 3√21 and 7√21 is 10√21.