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