Convert the following rectangular equations into polar equations.

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

$r = a\cos(\theta)$;
$a =$ .

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

$r = \frac{\cos(a\theta)}{\cos(b\theta)}$;
$a =$ , $b =$ .

(c) $x^4 - y^4 = xy$

$r^2 = a\tan(b\theta)$;
$a =$ , $b =$ .