قضیه استوارت

${\displaystyle b^{2}=p^{2}+y^{2}-2py\cos {\theta }\,}$ 

${\displaystyle c^{2}=p^{2}+x^{2}-2px\cos {180-\theta }\,====c^{2}=p^{2}+x^{2}+2px\cos {\theta }\,}$ 

${\displaystyle xb^{2}=xp^{2}+xy^{2}-2pxy\cos {\theta }\,}$ 

${\displaystyle yc^{2}=yp^{2}+yx^{2}+2pxy\cos {\theta }\,}$ 

${\displaystyle xb^{2}+yc^{2}=(x+y)p^{2}+xy(x+y)\,}$