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						Geometry Problem 1120: Isosceles Right 
						Triangle, 120 Degree, Angle, Equilateral, Metric 
						Relations. Level: High School, SAT Prep, 
						Honors Geometry, College, Math Education
				
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				The figure below shows an isosceles right triangle ABC. 
				D is a point so that angle ADC = 120 degree. E is on CD extended 
				so that angle BEC = 120 degree. BE extended meets AD at F. If AD 
				= d, CE = e, and BF = f, prove that (1) triangle DEF is 
				equilateral; (2) 
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