在一条河流的东岸有一城市E,河流西岸点B出有一林场,点A是一个移动沙漠的边缘点.沙漠由点A沿直线AC方向自西向东移动,将影响E市的环境.现计划自点B起沿直线BC方向修建一定宽度的一条固沙

在一条河流的东岸有一城市E,河流西岸点B出有一林场,点A是一个移动沙漠的边缘点.沙漠由点A沿直线AC方向自西向东移动,将影响E市的环境.现计划自点B起沿直线BC方向修建一定宽度的一条固沙
在一条河流的东岸有一城市E,河流西岸点B出有一林场,点A是一个移动沙漠的边缘点.沙漠由点A沿直线AC方向自西向东移动,将影响E市的环境.现计划自点B起沿直线BC方向修建一定宽度的一条固沙防护林,已测得AB=50km,林场B到沙漠移动方向AC的距离为30km,如果沙漠每年移动8km,每年营造防护林6km,要想在沙漠边缘移动C点时营造好BC段的防护林.
求营造BC段防护林需要多少年?

在一条河流的东岸有一城市E,河流西岸点B出有一林场,点A是一个移动沙漠的边缘点.沙漠由点A沿直线AC方向自西向东移动,将影响E市的环境.现计划自点B起沿直线BC方向修建一定宽度的一条固沙
1.需要X年 2.30÷3=10〔年〕
过点B作BD⊥AC于点D 40÷8=5〔年〕
∵∠ADB=90° 10﹥5
在直角三角形ADB中 ∴不能挡住沙漠移动
AD的平方=50的平方-30的平方=1600
∴AD=40km
在直角三角形BCD中
BC的平方=BD的平方+CD的平方
6X的平方=〔8X-4〕的平方+30的平方
∴X1=18,X2=5〔不合题意,舍去〕
5×6=30cm=BD

最好给我一个图

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