计算: 2021 0 + 3 - 1 ⋅ 9 - 2 sin 45 ° .
计算: (1); (2).
计算:.
计算 (1) (2)
计算 (1) (2)-
如图所示,已知AB∥CD,AB=CD,BF=CE,求证:AE=DF.