Sure, let's use the remainder theorem and the given answer to complete this proof step-by-step.
1. If [tex]\(x = -5\)[/tex] is a root of [tex]\(f(x)\)[/tex], then [tex]\((x + 5)\)[/tex] must be a factor of [tex]\(f(x)\)[/tex].
2. Find the remainder of [tex]\(f(x)\)[/tex] when divided by [tex]\((x + 5)\)[/tex].
3. The result of this operation is 0.
4. Thus, [tex]\((x + 5)\)[/tex] is a factor of [tex]\(f(x)\)[/tex].
5. Therefore, [tex]\(x = -5\)[/tex] is a root of [tex]\(f(x)\)[/tex].