矩形ABCD中,AD=6cm,AB=4cm,点E沿A往D方向在线段AD上移动点F沿D到A方向在线段DA上移动,如题,接下去是：速度都是2cm/s.如果E,F亮点同时分别从A、D出发,且当E移动到D点时停止.设运动时间为t秒①当四

矩形ABCD中,AD=6cm,AB=4cm,点E沿A往D方向在线段AD上移动点F沿D到A方向在线段DA上移动,如题,接下去是：速度都是2cm/s.如果E,F亮点同时分别从A、D出发,且当E移动到D点时停止.设运动时间为t秒①当四
矩形ABCD中,AD=6cm,AB=4cm,点E沿A往D方向在线段AD上移动点F沿D到A方向在线段DA上移动,
如题,接下去是：速度都是2cm/s.如果E,F亮点同时分别从A、D出发,且当E移动到D点时停止.设运动时间为t秒
①当四边形BCFE的面积是矩形的四分之三是,求t的值
②当t为何值,BCEF的对角线BF与CE的夹角是90°

矩形ABCD中,AD=6cm,AB=4cm,点E沿A往D方向在线段AD上移动点F沿D到A方向在线段DA上移动,如题,接下去是：速度都是2cm/s.如果E,F亮点同时分别从A、D出发,且当E移动到D点时停止.设运动时间为t秒①当四
题是不是错了,当E到D时F同时到达A啊 矩形是定的,路程是定的,速度是定的,那么时间也是定的啊.
貌似要是中间一个时间的话,那么第一提示等腰梯形BCFE的面积是（6+EF）x4/2=6x4x0.75解得EF=3所以E和F各运动了1.5cm所以t=0.75秒
第二题：
如果BF与CE成直角,设焦点为0,那么三角形BOC为等腰直角三角形,O到BC线的距离等于BC的一半为3cm,因此O到EF的距离为1cm.同样三角形OEF也为等腰直角三角形,EF/BC=1/3得EF=2cm,所以EF各运动了2cm所以t=1秒

after the car hit a pedestrian escape ,mercurial vapor, followed with four cars collided , causing two deaths and two injuries, Mercedes-Benz car hit the tree burned down , the Li Shilan surrendered (...

全部展开

after the car hit a pedestrian escape ,mercurial vapor, followed with four cars collided , causing two deaths and two injuries, Mercedes-Benz car hit the tree burned down , the Li Shilan surrendered ( January 20,nike mercurial vapor, newspaper reports ) .

process for the incident , Li Shilan said at his trial fell asleep while driving , to be greeted by a large truck , the lights blink of an eye , could not find the brake . After the incident,scarpe nike mercurial, Li Shilan paid 120 million yuan compensation from the victims .

court that Li Shilan in the event of the first car to escape after the accident , and in the process of driving the escape car crash more cars , causing two deaths and two minor injuries , constituted the crime of endangering public safety . In view of its initiative to surrender after the crime , and actively damages , therefore lighter made ??the above decision.

After the verdict , Li Shilan stretch appeal .

收起