3） 当CQ=BC 时 T= BC/2= 3秒当 CQ=BQ时 CQ= BC/2COS∠C = 3/(3/5)= 5 T=CQ/2 =2.5miao当 BC=BQ 时 CQ= 2BC *COS∠C = 2*6*3/5 =36/5 T= 18/5
2小题是4秒
