∵AB=AC，∴∠B=∠C，设∠B=∠C=α，则∠BAC=180°-2α，∵CD=AD，∴∠DAC=∠C=α，∵AB=BD，∴∠BAD=1/2(180°-∠B)=90°-1/2α，∴∠BAC=∠BAD+∠DAC=90°+1/2α，∴180°-2α=90°+1/2α，5/2α=90°，α=36°，即∠B=36°。
