证明：（1）∵DE平分∠CDA，∴∠ADE=∠EDC，而∠ADE=∠AED，∴∠EDC=∠AED，∴AB∥CD；（2）∵BF平分∠CBA，∴∠ABF= 1 2 ∠ABC，∵∠AED=∠ADE= 1 2 ∠ADC，而∠CDA=∠CBA，∴∠AED=∠ABF，∴DE∥BF．
