∫ad is the bisector of ∠BAC, ∴∠DAE=∠DAC,
Because AD is male marginal,
∴△ADE≌△ADC,(S,A,S),
∴DE=CD,
In the triangular bed, BE=AB-AE=AB-AC,
BD-DC=BD-DE, where be > BD-de,
∴ ab-AC > BD-DC (in a triangle, the difference between two sides is smaller than the third side).