請問2兀r x4+2x兀x r x r=90兀等於多少?
回答 (4)
2007-05-26 12:58 am
✔ 最佳答案
2兀r x4+2x兀x r x r =90兀8r+2r^2=90
r^2+4r-45=0
(r-5)(r+9)=0
所以,r=5或r=-9
參考: me
2007-05-26 8:55 am
(2pi r)(4)+(2pi r^2) = 90pi
8pi r+2pi r^2 = 90pi
pi(8r+2r^2) = 90pi
2r^2+8r = 90
2r^2+8r-90 = 0
(2r+18)(r-5) = 0
r = -9 or 5
8pi r+2pi r^2 = 90pi
pi(8r+2r^2) = 90pi
2r^2+8r = 90
2r^2+8r-90 = 0
(2r+18)(r-5) = 0
r = -9 or 5
參考: 自己
2007-05-26 4:14 am
2兀r x4+2x兀x r x r =90兀
8兀r+2兀r^2 =90兀
2兀r(4+r)=90兀
4+r=90兀÷2兀r
4+r=45÷r
r=5
2007-05-25 20:19:00 補充：
中間冇打4+r=45÷r4r+r×r - 45=0 r^2+9r-5r-45=0r(r+9)-5(r+9)=0(r-5)(r+9)=0r=5 or -9
8兀r+2兀r^2 =90兀
2兀r(4+r)=90兀
4+r=90兀÷2兀r
4+r=45÷r
r=5
2007-05-25 20:19:00 補充：
中間冇打4+r=45÷r4r+r×r - 45=0 r^2+9r-5r-45=0r(r+9)-5(r+9)=0(r-5)(r+9)=0r=5 or -9
參考: me
收錄日期: 2021-04-13 00:44:40
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070525000051KK02322