Let's take a look at a perfect square trinomial.
\((x+7)^2\)
We can distribute this expression to get \(x^2+14x+49\).
An important relation to recognize here is that the constant is the square of half of the x value.
Now, if we wanted to add a number to \(x^2+16x\) to make a perfect square trinomial, we could have the value of x and then square it.
Half of 16 is 8, and 8 squared is \(\boxed{64}\)
