**1. Is the angle in a triangle in a semi-circle always equal to 90 ^{o}?**

Yes, the angle not on the diameter is always 90

^{o}

**2. Is the angle at the centre of a circle always twice the size of the angle at the circumference?**

Yes, providing both angles are in the same segment or same side of the circle.

**3. Are angles on the same arc always equal?**

Yes, providing they touch the circumference and start and finish on the same arc.