2.
如图,在Rt△ABC,∠ACB=90°,现将Rt△ABC沿AE折叠,使AB边与AC边重合,B点落在B′处,在线段AE上取点F,使点F到AC,BC的距离相等,连接B′F,则∠B′FE的度数为( )
| A. | 30° | B. | 36° | C. | 45° | D. | 60° |
17.已知xy=4,x-y=5,则x2+3xy+y2=( )
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| A. | 54 | B. | 45 | C. | -54 | D. | -45 |