5 step solution
1. Divide AOB in half and use right triangle trigonmetry to find the base and height. (Alternative method, you can use law of cosines to find AB then proceed with Heron's formula)
2. Knowing the base and height, you can find the area of triangle AOB.
3. Find the area of the major portion of the circle that contains major arc AB
4. Add the area of the major portion and triangle together. Subtract that from the total circle area.
5. Your result is your answer.