直线的极坐标方程:
x = x 0 + r cos θ x= x_0 + r\cos \theta x=x0+rcosθ
y = y 0 + r sin θ y= y_0 + r\sin \theta y=y0+rsinθ
x cos θ = x 0 cos θ + r cos 2 θ x \cos \theta =x_0 \cos \theta + r \cos^2 \theta xcosθ=x0cosθ+rcos2θ
y sin θ = y 0 sin θ + r sin 2 θ y \sin \theta =y_0 \sin \theta + r \sin^2 \theta ysinθ=y0sinθ+rsin2θ
x cos θ + y sin θ = x 0 cos θ + y 0 sin θ + r x \cos\theta + y \sin \theta =x_0 \cos \theta + y_0 \sin \theta + r xcosθ+ysinθ=x0cosθ+y0sinθ+r
若 x 0 = 0 , y 0 = 0 , 则 : x_0 =0,y_0 = 0,则: x0=0,y0=0,则:
x cos θ + y sin θ = r x \cos\theta + y \sin \theta = r xcosθ+ysinθ=r