Combine parallel lines, isosceles triangles, ratios and bisectors

Answer: 52

1. ∠BDE and ∠ABC sum to 180∘ because DE ∥ BC.
2. Thus 5x+95=180, giving x=17.
3. Each base angle is 38∘.
4. The apex is 180−2×38=104∘, and half is 52∘.

Answer: 50

1. Angle C=180×94​=80∘.
2. In triangle AIB, angles A and B are halved
3. ∠AIB=180−2180−C​=90+2C​.
4. The smaller angle between the complete lines is its supplement, 90−2C​=50∘.

Answer: 67

1. ∠BDE and ∠ABC sum to 180∘ because DE ∥ BC.
2. Thus 5x+135=180, giving x=9.
3. Each base angle is 23∘.
4. The apex is 180−2×23=134∘, and half is 67∘.