As shown in the figure, take the waist ab of the isosceles triangle ABC as the diameter to draw a semicircle o, intersecting AC with E and BC with D Verification: 1. D is the midpoint of BC 2. If the angle BAC = 50 degrees, calculate the degree of arc BD

As shown in the figure, take the waist ab of the isosceles triangle ABC as the diameter to draw a semicircle o, intersecting AC with E and BC with D Verification: 1. D is the midpoint of BC 2. If the angle BAC = 50 degrees, calculate the degree of arc BD

(1) It is proved that: AB is the diameter, so ∠ bad is the circumference angle of the diameter, so ∠ bad = 90, ad ⊥ BC because AB = AC, so ad is the height on the bottom edge BC, and it is also the middle line on the bottom edge, so D is the midpoint of BC. (2) d is the midpoint of BC, according to the three lines of isosceles triangle, ad is also the bisector of ∠ BAC angle with ∠ bad = ∠ BAC / 2 = 25