为了估算河的宽度，小明画了测量示意图（如图5）.若测得BD =120m，DC =60m，EC =50m，则两岸间的距离AB等于 m.
=_________________ .
="_______________" ;
若与a互为相反数，则a=________.
________;
=_________________ .
="_______________" ;
与a互为相反数，则a=________.
________;
粤公网安备 44130202000953号