The sign of a product (x-a)(x-b)(x-c)... or quotient follows the wavy curve method. Key rules: (1) Odd number of negative factors → product is negative. (2) Even number → positive. (3) At each simple root, sign changes. (4) At repeated (even) root, sign doesn't change. (5) A quotient has the same sign as the corresponding product, but is undefined at denominator zeros.