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.

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In algebra, δ is used as a discriminant to represent the root of an equation. Discriminant of quadratic equation in one variable: δ = b? -4ac, when δ > 0, the equation has two unequal real roots; When δ = 0, the equation has two equal real roots; When δ