Which value must be added to the expressionx2+16x to make it a perfect-square trinomial?

Step-by-step explanation:

Please write  x^2+16x  or  x²+16x  to indicate the exponentiation.

To rewrite  x²+16x  as a perfect square trinomial:

1) Take half of the coefficient of x, that is, half of 16, which is 8

2) Square this result:  8² or 64

3) Starting with x²+16x again, add 64 and then subtract 64 to get a trinomial expression equivalent to x²+16x:

x²+16x + 64 - 64

4) Rewrite the first three terms as the square of the binomial x + 8:

(x + 8)² - 64  

Here (x + 8)² is a perfect square trinomial.

72 is the answer to this problem