Write each equation in polar coordinates. Express as a function of $.$ Assume that $r>0.($In your answer, type theta for $.)$

$($a$)y=1$

$r=$

$($b$)x^2+y^2=2$

$($c$)x^2+y^2+x=0$

$r=$

$($d$)x^2(x^2+y^2)=2y^2$