Explicație pas cu pas:
notăm EG ∩ FH = {M}
[tex]\measuredangle {EMH} = \frac{arc(EAH) + arc(FCG)}{2}
\\ = \frac{arc(EA) + arc(AH) + arc(FC) + arc(CG)}{2} \\ = \frac{ \frac{arc(AB)}{2} + \frac{arc(DA)}{2} + \frac{arc(BC)}{2} + \frac{arc(CD)}{2} }{2} \\ = \frac{arc(AB) + arc(BC) + arc(CD) + arc(DA)}{4} \\ = \frac{360 \degree}{4} = 90 \degree[/tex]
[tex] \implies \bf EG \perp FH[/tex]
