Answer: A Yes
The polynomial remainder theorem says when we divide polynomial f(x) by x-a we'll get remainder f(a).
f(x)=x^3-3x^2-31x-72
f(8)=8^3-3(8^2)-31(8)-72
f(8)=512-3(64)-31(8)- 72 = 512-192-248-72= 0
Since f(8)=0 that means x-8 has a remainder zero when divided by f(x). In other words, it's a factor of f(x).
