Attachment 34446

Did they make a mistake on line two, with x(x-a)?? [When I multiplied out, i got x(x+a), ending up with the locus as a circle with centre (-a/2, b/2) instead of (a/2, b/2)]

also, is there supposed to be a restriction on the locus? like excluding (a,0) (because z =/ a on the denominator)

Thanks!