2=(3x+7y)^2-x2=(3x+7y)2−x
9x^2+42xy+49y^2-x=29x2+42xy+49y2−x=2
After using x=rcos(theta)x=rcos(θ) and y=rsin(theta)y=rsin(θ) transormation,
9r^2(cos(theta))^2+42r^2*cos(theta)*sin(theta)+49r^2(sin(theta))^2-rcos(theta)=29r2(cos(θ))2+42r2⋅cos(θ)⋅sin(θ)+49r2(sin(θ))2−rcos(θ)=2
9r^2*(1+cos(2theta))/2+21r^2*sin(2theta)+49r^2(1-cos(2theta))/2-rcos(theta)=29r2⋅1+cos(2θ)2+21r2⋅sin(2θ)+49r21−cos(2θ)2−rcos(θ)=2
29r^2-20r^2cos(2theta)+21r^2sin(2theta)-rcos(theta)-2=029r2−20r2cos(2θ)+21r2sin(2θ)−rcos(θ)−2=0