WOLFRAM|DEMONSTRATIONS PROJECT

A Congruent Angle inside the Incircle

​
∠ABC
≈
75.93°
∠DEF
≈
75.93°
Let ABC be a triangle and let O be the center of the incircle. Let E be the point of tangency of the incircle with AC. Let AO and CO intersect the line drawn through the other two points of tangency at F and D, respectively. Then
∠ABC=∠DEF
.