Note: if you cannot remember how to utilise trigonometry in a circle, revise notes for 2.4 Applications of Trigonometry and Pythagoras Theorem.

Note: if you cannot remember how to calculate arc length, revise notes for 2.1 Circles and Arcs.

### Great Circles

- A circle drawn on the surface of a sphere whose radius is
**equal**to that of the sphere is known as a**great circle**.

### Distance Between Points on a Great Circle

- For two points on a great circle, the path corresponding to the
**shortest****distance**between those two points is an**arc**. We can use our understanding of arc length (from notes 2.1 Circles and Arcs) to solve for the shortest distance.