does not contain any powers higher than 1. A quadratic equation contains a variable that's highest power is 2. For example: y = x + 3 is a linear equation and y = x 2 + 3 x is a quadratic equation.

Peter Zadrozny, Analytic Derivatives for Estimation of Discrete-Time, Linear-Quadratic, Dynamic, Optimization Models, Econometrica, Vol. 56, No. 2 (Mar., 1988), pp ...

The conventional linear/quadratic/Gaussian assumptions are modified in that minimisation of the expectation of cost G defined by (2) is replaced by minimisation of the criterion function (5). The ...

Simultaneous equations with one linear and one quadratic - Higher tier A linear equation does not contain any powers higher than 1. A quadratic equation contains a variable, the highest power of ...