Key idea: Division Algorithm for polynomials
**Theorem**: For polynomials p(x) (dividend) and g(x) ≠ 0 (divisor), there exist UNIQUE polynomials q(x) (quotient) and r(x) (remainder) such that
p(x)=q(x)⋅g(x)+r(x),
where either r(x)=0 or deg r(x) < deg g(x).∗∗Mechanism**: long division of polynomials, exactly analogous to integer long division.
**Use case**: if you know one zero (or factor) of a higher-degree polynomial, divide it out to get a lower-degree quotient — then factor that.
**Example**: p(x)=x3−3x2−x+3. Try x=1:p(1)=0 → (x−1) is a factor. Divide: p(x)÷(x−1)=x2−2x−3=(x−3)(x+1). So p(x)=(x−1)(x−3)(x+1).