geometry problem(9) Geometry problem below was found in Facebook group "PI love math". AD=DB Question: prove that x=22.5 The proof step 1: draw perpendicular bisector of AB. E is intersection with BC. draw AE. LDAE=LDBE=x LAEC=x+x=2x.....(exterior angle of ΔABE) LCAE=2x Conclusion: AC=EC step 2: draw perpendicular bisector of AE, F is intersection with extended DE. draw FA. LAEF=90-x LEFC=LAFC=x LDAF=90-2x step 3: observe ΔADF FC is bisector of interior angle F. DC is bisector of exterior angle D. conclusion: AC is bisector of exterior angle A. step 4: observe angles at point A. 3x + 3x + 90-2x = 180 4x=90 x=22.50