1. Find the ratio of the areas of two circles with radii 3cm and 4cm respectively.
2.If the diameter of a circle is doubles, hoe does its area change?
3. A cicrular lawn of diameter 18m is surrounded by a path of 1m wide. Find the area of the path. (Express your answer in terms ofπ )
f.2 maths 20分
2008-05-28 1:11 am
回答 (2)
2008-05-28 2:03 am
✔ 最佳答案
1. The ratio of the areas of two circles:3 x 3 x 3.14 : 4 x4 x3.14
= 3 x 3 : 4 x 4
= 9 : 16
3. The radius of the path with lawn:
(18 2)/2 = 10m
So, the area of the path:
10 x 10 x 3.14 - 9 x 9 x 3.14
= 314 - 254.34
= 59.66m square
2008-05-27 18:09:28 補充：
第三題應該是:
10 x 10 x π - 9 x 9 x π
= 100π- 81π
= 19π
參考: 自己... 希望無計錯~ ^^
2008-05-28 1:40 am
1 3^2*π:4^2*π=9:16
2 assume original diameter is d,
Original area:d^2*π
Enlarged area:(2d)^2*π=4d^2*π
It becomes 4 times of original size
3 20^2*π-18^2*π=400π-324π=76π
2 assume original diameter is d,
Original area:d^2*π
Enlarged area:(2d)^2*π=4d^2*π
It becomes 4 times of original size
3 20^2*π-18^2*π=400π-324π=76π
收錄日期: 2021-04-23 17:55:21
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