P_1=(1,pi/4)" "P_2=(-4,(3pi)/2)
r_1=1" "theta_1=pi/4
r_2=-4" "theta_2=(3pi)/2
"distance between two points given in the polar coordinate system"
"is described as "Delta s=sqrt(r_1^2+r_2^2-2*r_1*r_2*cos(theta_2 - theta_1))
Delta s=sqrt(1^2+(-4)^2-2*1*(-4)*cos((3pi)/2 -pi/4)
Delta s=sqrt(1+16+8*cos(6pi-pi)/4)
Delta s=sqrt(17+8*cos((5pi)/4)
cos((5pi)/4 )=-0,7071067812
Delta s=sqrt(17-8*0,7071067812)
Delta s=sqrt(17-5,66)
Delta s=sqrt(11,34)
Delta s=3,37 " unit"