∵EF垂直平分AD
∴AE=DE
∠EAD=∠EDA,(1)
∵AD平分∠BAC
∴∠BAD=∠CAD,(2)
∵∠EAB=∠EAD+∠BAD,
∠ECA=∠EDA+∠CAD,
∴∠EAB=∠ECA,
又∠AEC是公共角,
∴△BAE∽△ACE
∴AB:AC=BE:AE AB:AC=AE:CE
∴AB²:AC²=BE:CE
∵EF垂直平分AD
∴AE=DE
∠EAD=∠EDA,(1)
∵AD平分∠BAC
∴∠BAD=∠CAD,(2)
∵∠EAB=∠EAD+∠BAD,
∠ECA=∠EDA+∠CAD,
∴∠EAB=∠ECA,
又∠AEC是公共角,
∴△BAE∽△ACE
∴AB:AC=BE:AE AB:AC=AE:CE
∴AB²:AC²=BE:CE