Explanation:
Using the remainder theorem when , when the value of x + 2 is substituted into the polynomial if it's a factor it will produce a result of zero else any number will prove that it's not a factor.
So we have
x + 2 = 0
x = - 2
Substitute the value of x into the polynomial
That's

Since it leaves a remainder of - 16 (x + 2) is not a factor of the polynomial
Hope this helps you