For 0<a<1, let R_a be the rectangle whose side lengths are a and 1. Show that every rectangle is conformally equivalent to one and only one of this rectangles.

Hint: use the schwarz reflection principle and the fact that every ring in C (subset whose complement has two components) is conformally equivalent to one and only one o: C/{0}, D/{0} or Ar={z in C : 1 < |z| < r}

Thanks