Concept:Since ∣AB∣=∣AC∣, triangle ABC is isosceles, so the base angles ∠ABC and ∠ACB are equal. Use the straight-line angle property to find ∠ACD.Explanation:Let ∠ACB=∠ABC=x.In △ABC, the sum of angles is 180∘:x+x+50∘=180∘2x+50∘=180∘2x=130∘x=65∘So ∠ACB=65∘.Since BC is produced to D, ACD is a straight line, giving:∠ACD=180∘−∠ACB∠ACD=180∘−65∘=115∘Answer:115∘Option A.
