For a cubic polynomial \boldsymbol{p(x) = ax^3 + bx^2 + cx + d}, if \boldsymbol{\alpha}, \boldsymbol{\beta}, and \boldsymbol{\gamma} are the zeroes, then:
\displaystyle\boldsymbol{\alpha + \beta + \gamma = -\frac{b}{a}}
This is the sum of zeroes expressed in terms of the coefficients of \boldsymbol{x^3} and \boldsymbol{x^2}.