如图，A，B，C点在⊙O上，若∠ACB = 36°，则∠AOB的度数为 __ 。---Chart/Diagram Description: * Type: Geometric figure (Circle diagram). * Main Elements: * Points: Point O is the center of the circle. Points A, B, and C are located on the circumference of the circle. * Lines: Line segments connect the center O to points A and B (OA and OB, which are radii). Line segments connect points A to B (AB), A to C (AC), and B to C (BC), forming chords of the circle and the sides of triangle ABC. * Shapes: A circle with center O. Triangle OAB is formed by two radii and a chord. Triangle ABC is inscribed in the circle, formed by three chords. * Relative Position and Direction: Point O is at the center. Points A, B, and C are distinct points on the circle's boundary. Segment OA and OB connect the center to the circumference. Segments AB, AC, BC connect points on the circumference. * Labels and Annotations: Points O, A, B, C are labeled. **Note:** The image contains only the diagram. There is no accompanying question stem, options, or other text.