ax^2+bx+c =0
where a ≠ 0. (For a = 0, the equation becomes a linear equation.)
The letters a, b, and c are called coefficients: the quadratic coefficient a is the coefficient of x^2, the linear coefficient b is the coefficient of x, and c is the constant coefficient, also called the free term or constant term.
Quadratic equations are called quadratic because quadratus is Latin for "square"; in the leading term the variable is squared.
Quadratic formula
A quadratic equation with real or complex coefficients has two (not necessarily distinct) solutions, called roots, which may or may not be real, given by the quadratic formula:
are solutions.
Simply put, ± means 'plus or minus' as equation possibilities.
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