1. State the problem.
Use the Factor Theorem to determine whether $x-2$ is a factor of $f(x)=x^3-4x^2+x+6$, and to factor $f(x)$ completely.
2. Formula and important rules.
The Factor Theorem states that $f(a)=0$ if and only if $x-a$ is a factor of $f(x)$.
The Remainder Theorem says the remainder when dividing $f(x)$ by $x-a$ equals $f(a)$.
Synthetic division is a quick method to divide a polynomial by a linear factor and obtain the quotient and remainder.
3. Evaluate $f(2)$ to test the candidate factor.
Compute $f(2)=8-16+2+6$.
Simplify to $f(2)=0$.
Therefore $x-2$ is a factor of $f(x)$ by the Factor Theorem.
4. Divide $f(x)$ by $x-2$ using synthetic division to find the quotient.
Coefficients: $1, -4, 1, 6$.
Synthetic division steps: bring down $1$; multiply by $2$ gives $2$; add to $-4$ gives $-2$.
Multiply $-2$ by $2$ gives $-4$; add to $1$ gives $-3$.
Multiply $-3$ by $2$ gives $-6$; add to $6$ gives remainder $0$.
So the quotient polynomial is $x^2-2x-3$.
5. Factor the quadratic quotient.
Factor $x^2-2x-3$ as $(x-3)(x+1)$ because $-3+1=-2$ and $(-3)(1)=-3$.
6. Final factorization and check.
Combine the factors to get $f(x)=(x-2)(x-3)(x+1)$.
Optionally expand to check: $(x-2)(x-3)(x+1)=x^3-4x^2+x+6$ which matches the original polynomial.
Final answer: $f(x)=(x-2)(x-3)(x+1)$.
Factor Theorem
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