[tex]r=-8\sec\theta=-\dfrac8{\cos\theta}\implies r\cos\theta=-8[/tex]
Converting from rectangular coordinates to polar coordinates involves setting [tex](x,y)=(r\cos\theta,r\sin\theta)[/tex]. Since the left hand side matches [tex]x[/tex] perfectly, the equation's rectangular coordinate form is [tex]x=-8[/tex].
