A solid cylinder has radius r cm and height (r-2) cm
a)Find the total surface area of the cylinder, express the answer in terms of
圖片參考：http://www.learner.org/interactives/geometry/images/pi.gif
and r.
b) if the total surface are of the cylinder is less than 48
圖片參考：http://www.learner.org/interactives/geometry/images/pi.gif
CM^2 , find the range of the values of r.
Maths!!!!!!!!!!!!唔識做牙!
2010-09-24 5:21 am
回答 (2)
2010-09-24 5:46 am
✔ 最佳答案
As follows:圖片參考：http://i707.photobucket.com/albums/ww74/stevieg90/09-48.jpg
2010-09-23 21:56:02 補充：
我漏左個pi=.="
感謝雨後陽光兄你提醒...
2010-09-23 22:01:46 補充：
哈哈...用圖就有這個好處=0=
2010-09-24 5:49 am
a)total surface area :
2πr² + 2πr (r-2)
= 2πr (r + r - 2)
= 2πr (2r - 2)
= 4 π r (r - 1)
b)
4 π r (r - 1) < 48π
r (r - 1) < 12
r^2 - r - 12 < 0
(r - 4)(r + 3) < 0
_____(-3)_________0______(4)_____
- 3 < r < 4
But the height = r - 2 > 0 ,
r > 2
so
2 < r < 4
2010-09-23 22:00:23 補充：
你再次施展移形換影,偷天換日了無痕跡......勁^^
2πr² + 2πr (r-2)
= 2πr (r + r - 2)
= 2πr (2r - 2)
= 4 π r (r - 1)
b)
4 π r (r - 1) < 48π
r (r - 1) < 12
r^2 - r - 12 < 0
(r - 4)(r + 3) < 0
_____(-3)_________0______(4)_____
- 3 < r < 4
But the height = r - 2 > 0 ,
r > 2
so
2 < r < 4
2010-09-23 22:00:23 補充：
你再次施展移形換影,偷天換日了無痕跡......勁^^
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