Answer with explanation:
Polar Equation : An equation whose variables are polar coordinates.
Polar equation of a curve is denoted in terms of (r, theta).
Where,

x and y are abscissa and ordinate in x y plane.
Theta is angle made by line joining origin to point represented by , P(r, Theta) in Positive direction of X axis.
⇒r=Distance from origin to the point
Polar equation of Circle
⇒x²+y²=r²
x=r cos A
y=r sin A
Angle , A is made with positive direction of X axis from line joining origin to end point.