circles

• Area of circle: πr²
• Circumference of circle: 2πr
• area of semi circle: πr² divided by 2
• Area of quadrant: πr² divided by 4 or πr² x 90/360
• Length of arc: 2πr x x/360
• perimeter= length of arc + r+ r
• Area of sector: πr² x x/360