An integral equation that contains only one unknown (unary) and the highest order of the unknown is 2 (quadratic) is called unary quadratic equation.
The establishment of a quadratic equation with one variable must meet three conditions at the same time:
1. It is an integral equation, that is, both sides of the equal sign are algebraic expressions, if there is a denominator in the equation; And the unknown is on the denominator, then this equation is a fractional equation, not a quadratic equation. If there is a root sign in the equation and the unknown is within the root sign, then the equation is not a quadratic equation.
2. It contains only one unknown number;
The maximum number of unknowns is 2.
An integral equation with two unknowns whose terms are 1 is called a binary linear equation.