$P = w h^{2} 2 \times ( 1 + \sin \phi ) ( 1 − \sin \phi )$

$P = w h^{2} 2 \times ( 1 - \cos \phi ) ( 1 + \cos \phi )$

$P = w h^{2} 2 \times ( 1 - \sin \phi ) ( 1 + \sin \phi )$

$P = w h^{2} 2 \times ( 1 + \cos \phi ) ( 1 - \cos \phi )$