f.4 variations

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[匿名]

2010-07-30 2:50 am

the cost($C) of coating a plastic film onto a wooden hemisphere varies directly as the square of the radius (r cm) of the hemisphere.ir's given that the cost of coating a hemisphere of radius 6cm is $20

(a)find an eqn. connecting C and r

(b)(i)find the radius of the hemisphere id the cost of coating is $45
(ii)find the cost of coating a hemisphere of radius 0.18m

更新1:

(b)(ii)答案係$180wo

回答 (1)

用戶2053

2010-07-30 3:15 am

✔ 最佳答案

a)C = k r^2When C = 20 ,20 = k 6^2k = 5/9SoC = (5/9)r^2bi)45 = (5/9)r^281 = r^2r = 9The required radius = 9mbii)C = (5/9)(0.18)^2C = (5/9)(9/50)^2C = (1/10)(9/50)C = 9/500The required cost = $ 9/500

2010-07-29 19:46:29 補充：
Corrections :

bii)

C = (5/9)(18)^2 ......(0.18m = 18cm)

C = 180

The required cost = $ = 180

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