Find a polar equation for the curve represented by the given Cartesian equation.

1. x^2 - y^2 = 1

so I know x = rcos(-) , y = rsin(-)

[rcos(-)]^2 - [rsin(-)]^2 = 1

r^2[ (cos(-))^2 - (sin(-))^2 ) = 1

r^2 [ cos2(-) ] = 1

??

can someone show me how to do this.. am i doing this completely wrong? lol thanks..