() Circle volume = 4/3(π)(R3).

(2) area = (pi) (r 2).

(3) perimeter = 2(π)r

(4) The standard equation of a circle (x-a)2+(y-b)2=r2(a, B) is the center coordinate.

(5) general equation x2+y2+dx+ey+f = 0d2+E2-4f > 0。

2. Double angle formula

( 1)tan2a = 2 tana/( 1-tan2a)ctg2a =(ctg2a- 1)/2c TGA .

(2)cos2a = cos2a-sin2a = 2 cos2a- 1 = 1-2 sin2a .

3. Half-angle formula

( 1)sin(a/2)=√(( 1-cosa)/2)sin(a/2)=-√(( 1-cosa)/2)。

(2)cos(a/2)=√(( 1+cosa)/2)cos(a/2)=-√(( 1+cosa)/2).

(3)tan(a/2)=√(( 1-cosa)/(( 1+cosa))tan(a/2)=-√(( 1-cosa)/(( 1+cosa))。

(4)ctg(a/2)=√(( 1+cosa)/(( 1-cosa))ctg(a/2)=-√(( 1+cosa)/(( 1-cosa))。

4. Parabola

(1) parabola: y=ax*+bx+c means that y equals the square of ax plus bx plus C.

A>0, parabolic opening upward; At a & lt0°, the parabolic opening is downward; When c=0, the parabola passes through the origin; When b=0, the axis of symmetry of parabola is the Y axis.

(2) Vertex y=a(x+h)*+k is Y equals A times the square of (x+h) +k, -h is X of vertex coordinates, and K is Y of vertex coordinates, which is generally used to find the maximum and minimum values.

(3) Parabolic standard equation: y 2 = 2px, which means that the focus of parabola is on the positive semi-axis of X, and the focal coordinate is (p/2,0).

(4) The alignment equation is x=-p/2. Because the focus of parabola can be on any half axis, there is a standard equation for * * *: y 2 = 2pxy 2 =-2pxy 2 =-2pxy.