Geometry Problem 1274

Elements: Isosceles Triangle, 80-20-80 Degrees, Area, Inradius, Circumradius, Angle Bisector, Metric Relations, Measurement

In an isosceles triangle ABC, the measure of angle B is 20 degrees, AB = BC = a, and AC = b. Prove that (1) a³ + b³ = 3a²b, (2) ; (3) ; (4) ; (5) .
This entry contributed by Sumith Peiris, Moratuwa, Sri Lanka.

See also:
Geometry problem 1271 in motion. 

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