A:There are four
B:There are six
如图,在△ABC中,∠ACB=90°,AC=BC,P为三角形内部一点,且PC=3,PA=5,PB=7,则△PAB的面积为____
在直角梯形ABCD中,AB∥CD,∠ABC=90°,AB=2BC=2CD,则cos∠DAC=( )