Square ABCD, AE + CF = EF, verification ∠ EDF = 45 degree

Square ABCD, AE + CF = EF, verification ∠ EDF = 45 degree

As shown in the figure, rotate ⊿ DCF clockwise 90 ≌ around d to ⊿ DAG, ≛ Ge = GA + AE = FC + AE = EF, ≛ DG = DF, ≌ DGE ≌ DFE (SSS), ≌ GDE ≌ FDE, GDE + FDE ≌ GDF = 90 ≌ EDF ≌