You don't want 'x' in the polar form. The arguments
of the sin and cos should be angles.
You're doing great. You're already through the tough part.
You knew that x = r cos(α) and y = r sin(α) .
The correct equation for where you stopped is
x· y = r² · cos(α) · sin(α) = 1
You can simplify it a little if you remember the 'double-angle' equation:
sin(2α) = 2 · sin(α) · cos(α)
So cos(α) · sin(α) = (1/2) sin(2α)
and r² · cos(α) · sin(α) = 1
r² · sin(2α) = 2