Orthocentre angle relation – ∠BOC = 100° (O is orthocentre): In triangle ABC, O is the orthocentre. If ∠BOC = 100°, find ∠BAC.

Introduction / Context:A key property: in any triangle, the angle ∠BHC at the orthocentre H equals 180° − ∠A. Here, O plays the role of H.

Concept / Approach:Thus ∠BOC = 180° − ∠A ⇒ ∠A = 180° − ∠BOC.

Step-by-Step Solution:

Final Answer:80°