To convert the rectangular equaton to polar form, we use
[tex]x=r\cos (\theta),y=r\sin (\theta),r^2=x^2+y^2[/tex]
we replace x^2 + y^2 by r^2,
[tex]r^2-7ay=0[/tex]
Then, we replace y,
[tex]\begin{gathered} r^2-7a(r\sin (\theta))=0 \\ r^2=7a\cdot r\sin (\theta) \\ r\cdot r=7a\cdot r\sin (\theta) \\ r=\frac{7a\cdot r\sin (\theta)}{r} \\ r=7a\cdot\sin (\theta) \end{gathered}[/tex]
