r=y2+x2
y=13x²+4x=r⋅cosϕr=(13r2cos2ϕ+4)2+r2cos2ϕ
r=169r4cos4ϕ+104r2cos2ϕ+16+r2cos2ϕ
r=169r4cos4ϕ+105r2cos2ϕ+16
r2=169r4cos4ϕ+105r2cos2ϕ+16
0=169r4cos4ϕ+105r2cos2ϕ−r2+16
0=169r4cos4ϕ+r2(105cos2ϕ−1)+16
z=r2
0=z2169cos4ϕ+z(105cos2ϕ−1)+16
z1,2=2⋅169cos4ϕ1−105cos2ϕ±(105cos2ϕ−1)2−4⋅169cos4ϕ⋅16
z1,2=2⋅169cos4ϕ1−105cos2ϕ±(105cos2ϕ)2−210cos2ϕ+1−64⋅169cos4ϕ
z1,2=338cos4ϕ1−105cos2ϕ±209cos4ϕ−210cos2ϕ+1
r1,2,3,4=±338cos4ϕ1−105cos2ϕ±209cos4ϕ−210cos2ϕ+1
V(ϕ)=r⋅(sinϕcosϕ)
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