Circles formula

Diameter = 2 x radius of circle.

Circumference of Circle = PI x diameter = 2 PI x radius
where PI = = 3.141592...

Area of Circle:
area = PI r²

Length of a Circular Arc: (with central angle )
if the angle is in degrees, then length = x (PI/180) x r
if the angle is in radians, then length = r x

Area of Circle Sector: (with central angle )
if the angle is in degrees, then area = (/360)x PI r²
if the angle is in radians, then area = ((/(2PI))x PI r²

Equation of Circle: (Cartesian coordinates)

for a circle with center (j, k) and ra

dius (r):

(x-j)^{^2} + (y-k)^{^2} = r^{^2}

Equation of Circle: (polar coordinates)

for a circle with center (0, 0

): r() = radius

for a circle with center with

polar coordinates: (c, ) and

radius a:
r² - 2cr cos( - ) + c² = a²

Equation of a Circle: (parametric coordinates)
for a circle with origin (j, k) and radius r:
x(t) = r cos(t) + j y(t) = r sin(t) + k