\overline{AB}

The derivative of a variable raised to a power is the product of the power and the expression, then you reduce the power by 1.

一元二次方程 y = ax^2+bx+c (a\ne 0 ) 有两个相同或不同的解, 即：

x_{1,2} = \dfrac{-b\pm\sqrt{b^2-4ac} }{2a}

The cubic equation without the quadratic term is in the form that is called depressed cubic equation.

x^3+px+q=0

y = ax^2+bx+c (a\ne 0 )

The arithmetic and geometric means inequality, or the AM–GM inequality, states that the arithmetic mean of a list of positive real numbers is greater than or equal to the geometric mean of the same list; and further, that the two means are equal if and only if every number in the list is equal to each other.

Cosine of the difference of two angles is equal to the product of cosine of the two angles plus the product of sine of the two angles.

The cosine of the double angle is equal to the square of cosine of the angle minus the square of sine of the angle.