Question

What is the product of the two integer values for $x$ for which $|x^2 - 16|$ is a prime number?

Answer 1

Answer:

-9

Step-by-step explanation:

x² -16 = (x -4)(x +4)

This magnitude of this product can only be prime if one of the factors is ±1. Any other integer value of x will produce a composite number (or zero).

... For x-4 = ±1, x = 3 or 5

... For x+4 = ±1, x = -3 or -5

The values of x that are ±3 both give |x²-16| = 7, a prime.

The values of x that are ±5 both give |x²-16| = 9, not a prime.

The two values of x that are of interest are x=-3 and x=3. Their product is ...

... (-3)·(3) = -9