The expression given to us is: x²+6x
Now, we know that the second term is twice the square root of the first and the last terms. Let us call the last term as
. Thus our given expression will become:
.
Now, since the middle term is 6x and since we know that the second term is twice the square root of the first and the last terms, therefore,


(By dividing both sides by 2x)
Therefore, the missing term is 3.