The principal of Square Roots
The quadratic equation
5x2 + 8x – 2 = 0
is said to be in standard form. The quadratic equation
5x2 = 2 – 8x
Is equivalent to the preceding, but it is not in standard form.
Quadratic Equation
An equation of the type ax2 + bx + c = 0, where a, b, and c are real-number constants and a > 0, is called the standard form of a quadratic equation.
The Principle of Square Roots
The solutions of the equation x = d are 
and –.
When d > 0, the solutions are two real numbers.
When d = 0, the only solution is 0.
When d < 0, the solutions are two imaginary numbers.