作AS⊥PQ,CT⊥MN,垂足分别为S,T.
由题意知,四边形ATCS为矩形, 所以AS=CT,SC=AT. 设这条河的宽度为x米. 在Rt△ADS中,因为, 所以. ······················································(2分) 在Rt△BCT中,因为, 所以. ······················································(3分) 因为SD+DC =AB+BT,所以,···············································(6分) 解得,即这条河的宽度为75米. ······················································(7分) (其它方法相应给分) |