put x=rcostheta,y=rsinthetax=rcosθ,y=rsinθ and solve
2=(8x-7y)^2-7x2=(8x−7y)2−7x
=>2=64x^2+49y^2-112xy-7x⇒2=64x2+49y2−112xy−7x
=>2=49(x^2+y^2)+15x^2-7x-xy⇒2=49(x2+y2)+15x2−7x−xy
=>2=49r^2(sin^2theta+cos^2theta)+15r^2sin^2theta-56.2r^2sinthetacostheta⇒2=49r2(sin2θ+cos2θ)+15r2sin2θ−56.2r2sinθcosθ
=>2=49r^2+15r^2sin^2theta-56r^2sin2theta⇒2=49r2+15r2sin2θ−56r2sin2θ
=>(15sin^2theta-56sin2theta+49)r^2-2=0⇒(15sin2θ−56sin2θ+49)r2−2=0