MC~~~~~~~~~~~~~

61.C
62.C
63.C
64.A
65.B
66.B

2007-07-26 17:10:52 補充：
61.Let r cm be the radius,then area=兀r^2 cm^2So 兀r^2=9兀r^2=9r=3 or -3(rejected)So, the radius is 3cm.Diameter=3cm x 2 = 6cmAnswer:C62.Arc AB=兀 x 4cm / 2 = 2兀cmArc BC=兀 x 2cm / 2 = 兀cmPerimeter=AB BC Arc AB Arc BC=4cm 2cm 2兀cm 兀cm=(3兀 6)cmAnswer:C

2007-07-26 17:11:20 補充：
63.Perimeter=AO BO Arc AB=21cm 21cm ArcAB=42cm ArcABLength of Arc AB 0So, Perimeter 42cm.The only answer which is larger than 42cm is C.Answer:C

2007-07-26 17:13:27 補充：
Explanation of Question 63 has some amendmentLine 3:Perimeter is larger than 42cm.Line 4:So, Perimeter is larger than 42cm.

2007-07-26 17:13:55 補充：
64.Let r cm be the radius.then area = 0.5兀r^2 cm^2i.e. 0.5兀r^2 = 32兀r^2 = 64r = 8 or -8 (rejected)So the radius is 8cm.Arc AB = 2兀(8cm)/2 = 8兀cmAB = 8cm x 2 =16cmPerimeter = Arc AB + AB = (8兀+16)cmAnswer:A

2007-07-26 17:14:08 補充：
65.Area of a whole circle = 兀(6cm)^2 = 36兀cm^2Area of the sector OAB = 36兀cm^2 x 3/4 = 27兀cm^2Area of each equal part = 27兀cm^2 / 5 =(27/5)兀cm^2Answer:B

2007-07-26 17:14:30 補充：
66.Area of sector OAB = 兀(4cm)^2 / 4 = 4兀cm^2Area of triangle OAB = 4cm x 4cm / 2 = 8cm^2Area of segment AB = 4兀cm^2 - 8cm^2 = (4兀 - 8)cm^2 Area of sector O2CD = 兀(8cm)^2 / 4 = 16兀cm^2

2007-07-26 17:14:37 補充：
Area of triangle O2CD = 8cm x 8cm / 2 = 32 cm^2Area of segment CD = 16兀cm^2 - 32cm^2 = (16兀 - 32)cm^2 Since we cannot find two parts which is in the ratio 1:2 , 1:8 and 1:兀.Therefore, answer cannot be A,C or D.Answer:B

C
C
C
A
B
B