Discovering Geometry Day 58
8.6 Areas of parts of
a Circle
§ Daily Openers
§ Check and go over homework
§ Make-up Quiz
8.6 Areas of Sectors, Segments, and Annulus
Area of a Circle
A = π · r 2
sector of a circle – the region between two radii and the intercepted arc.
segment of a circle – the region between a chord of a circle and the intercepted arc.
chord – a segment with endpoints on the circle.
annulus – the region between two concentric circles.
concentric – circles with the same center point.
éHow would you find the area of a sector?
éHow would you find the area of a segment? [10 bonus points]
éHow would you find the area of an annulus? [5 bonus points]
Ex. Find the shaded area? Ex. Find the shaded area?
Ex. Find the shaded area? Ex. Find the shaded area?
Ex. The shaded area is 24π. Ex. The shaded area is 36π.
Homework – page 455–456 #1–12 all, 15
Daily Openers – 1. A circle has an A= 20.25π, what is the diameter?
2. A circle has a C = 53.40707511, what is the Area?
3. Find the area of a regular decagon with an apothem of 6 cm.
and a side length of 8 cm.
4. The school is putting new tile in the cafeteria after 65 years.
The tile is 1yd by 1 yd. They are buying the cheapest tile available,
at $11.25 per square yard. The cafeteria is 150’х 75’. How much would
it cost?
5. Find the perimeter of the figure: