Over the complex numbers every polynomial factors: x² + 4 = (x + 2i)(x - 2i), and a polynomial of degree n has exactly n complex zeros counted with multiplicity. The Fundamental Theorem of Algebra says so, and the quadratic formula shows it for degree 2. Pascal's triangle gives the coefficients of (x + y)ⁿ, the Binomial Theorem. Rational expressions behave like fractions: add, subtract, multiply or divide two and you get another.