6.8 areas of circles & sectors p. 230. thm 6.20 – area of a circle – a = r2 * remember to...
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6.8 Areas of Circles & 6.8 Areas of Circles & SectorsSectors
p. 230p. 230
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Thm 6.20Thm 6.20 – – Area of a CircleArea of a Circle – –
A = A = rr22
* Remember to square the radius 1* Remember to square the radius 1stst, , then multiply by then multiply by !!
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ExEx: Find the area of circle C.: Find the area of circle C.
A = A = rr22
A = A = (3)(3)22
A = 9A = 9 cm cm22
OROR
28.27 cm28.27 cm22CC
3 cm3 cm
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ExEx: Find the diameter of circle C : Find the diameter of circle C if the area is 16if the area is 16 ft ft22..
A = A = rr22
1616 = = rr22
16 = r16 = r22
ðð16 = r16 = r
4 ft = r4 ft = r
So,So,
d = 8 ft.d = 8 ft.
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Sector of a CircleSector of a Circle• The region bounded by 2 radii & their The region bounded by 2 radii & their
intercepted arc.intercepted arc.
SectorSector
Also aAlso a
sectorsector
• Visually, it might remind you of a slice Visually, it might remind you of a slice of pizza or a piece of pie.of pizza or a piece of pie.
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Thm 6.21Thm 6.21 – – Area of a SectorArea of a Sector – –
2
360
r
measurearcA
o
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ExEx: Find the area of the small sector : Find the area of the small sector shown.shown.
135135oo11 m11 m
2
360
r
measurearcA
o
211360
135 o
o
A
121360
135A
2 55.142 mA
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ExEx: L & M are 2 pts. on a circle R with : L & M are 2 pts. on a circle R with r=50 cm & mr=50 cm & mLRM=150LRM=150oo. Find the areas . Find the areas
of the sectors formed by of the sectors formed by LRM.LRM.
2
360
r
measurearcA
oI
150150oo
II
IIII
2
360
r
measurearcA
oII
250360
150 IA
2 49.3272 cmAI
250360
210 IIA
2 49.4581 cmAII
LLMM
RR 50 cm50 cm