Delta formula: △ = b 2-4ac. Delta is the pronunciation of the fourth Greek letter, capitalized as δ and lowercase as δ. In mathematics or physics, the capitalized δ is used to represent the incremental symbol. And lowercase δ is usually used to represent variables or symbols in higher mathematics.

In algebra, δ is used as a discriminant to represent the root of an equation.

Discriminant formula of quadratic equation in one variable: δ = b2-4ac.

① When δ > 0, the equation has two unequal real roots.

② When δ = 0, the equation has two equal real roots.

③ When δ