### Glossary

• a quadratic equation or expression in $x$ contains an $x^2$ term but not $x^3$
• if there is more than one variable, quadratic includes the possibility that they are multiplied together in pairs but not in threes, for example $x^2+2y$, $xy-3$ and $x^2+y^2+3xy-y+1$ are all quadratic, but $x+y$, $x^2y$ and $x^3-y^2$ are not (the first is linear, the other two are cubic).