Given:
1=(-x+4)^2+(2y+9)^21=(−x+4)2+(2y+9)2
1=(-x+4)^2+(2(y+9/2))^21=(−x+4)2+(2(y+92))2
1=(-x+4)^2+4(y+9/2)^21=(−x+4)2+4(y+92)2
x=rcosthetax=rcosθ
y=rsinthetay=rsinθ
Substituting
1=(-rcostheta+4)^2+(2rsintheta+9)^21=(−rcosθ+4)2+(2rsinθ+9)2
1=r^2cos^2theta-8rcostheta+16+4r^2sin^2theta+36rsintheta+811=r2cos2θ−8rcosθ+16+4r2sin2θ+36rsinθ+81
r^2(cos^2theta+4sin^2theta)+r(-8costheta+36sintheta)+81-1=0r2(cos2θ+4sin2θ)+r(−8cosθ+36sinθ)+81−1=0
2r^2(cos^2theta+4sin^2theta)-2r(4costheta-18sintheta)+2(40)=02r2(cos2θ+4sin2θ)−2r(4cosθ−18sinθ)+2(40)=0
r^2(cos^2theta+4sin^2theta)-r(4costheta-18sintheta)+40=0r2(cos2θ+4sin2θ)−r(4cosθ−18sinθ)+40=0