How to draw a precise circular arc in Adobe Illustrator?

Question

Say, an arc with radius *r* centered at *o*, from angle *a* to angle *b*.I don't see how to use Arc tool in Adobe Illustrator this way. What's the best way to draw it?

Answer 1

Draw a circle with radius *r* from the center *o*, then separately draw an angle with its corner at the center, ensuring that the lines intersect the circle. Use Pathfinder > Divide or the the Scissors tool to segment out your arc.