Verwende sin2(φ)+cos2(φ)=1 und sin/cos=tan.
Falls du Klammern vergessen hast:
sin2(phi)/((cos(phi)+sin(phi))^ 2 - 1)
=sin2(phi)/(cos2(phi)+2cos(phi)sin(phi)+sin2(phi)- sin2(phi)-cos2(phi))
=sin2(phi)/(2cos(phi)sin(phi))
=sin(phi)/(2cos(phi))
=1/2 * tan(phi)
:-)