1.三角形ABC是等腰三角形,AC=BC,AB=18cm及其面積是58cm^2。求三角形ABC各內角的大小,準確至最接近的0.1度
2.梯形ABCD,AD平衡BC,AB=DC,AD=8cm,BC=18cm及AE=15cm。求BE,AB同角度B
3.梯形ABCD,AD平衡BC,角度B=62度,角度C=43度,CD=3cm及AD=1.5cm。求梯形ABCD的周界。
有幾條數唔識做
2008-03-12 7:55 am
回答 (2)
2008-03-13 2:38 am
✔ 最佳答案
1. http://i71.photobucket.com/albums/i141/natcny/m1.jpg設三角形的高度為h cm
(h x AB)/2 = 58
h x 18 = 116
h = 6.44
h/9 = tan∠CAB
∠CAB = 35.6°
∠CAB = ∠CBA (等腰三角形的底角)
∠CBA = 35.6°
∠CAB + ∠CBA + ∠ACB = 180° (三角形內角和)
∠ACB = 108.8°
2. (E是在此位置嗎?) http://i71.photobucket.com/albums/i141/natcny/m2.jpg
如是的:
BE = 18 - 8 = 10cm
AB^2 = BE^2 + AE^2 (畢氏定理)
AB^2 = 10^2 + 15^2
AB = 18.03 cm
tan∠ABE = 15/10
∠ABE = 56.31°
3. (圖是這樣嗎?) http://i71.photobucket.com/albums/i141/natcny/m3.jpg
如是:
CF/3 = cos43°
CF = 2.19 cm
DF/3 = sin43°
DF = 2.05 cm
2.05/BE = tan62°
BE = 1.09 cm
1.09/AB = cos62°
AB = 2.32 cm
周界=1.5+3+2.19+1.5+1.09+2.32
=11.6cm
建議下次附設圖方便知道形狀的資料
參考: myself(:
2008-03-12 5:30 pm
1)18h/2=58
h=58/9
tanC=(58/9)/9
C=72.8
180-72.8-72.8=B
B=34.4
2) 唔知E係邊所以答唔到不過角B就得
cosB=5/15
B=70.5
3)cos42=A/3
A=2.2
sin42=B/3
B=2
tan62=2/C
C=1.06
sin62=2/D
D=2.3
周界=2.3+1.06+1.5+2.2+3+1.5
=11.56
2008-03-12 09:31:06 補充：
希望你明白
h=58/9
tanC=(58/9)/9
C=72.8
180-72.8-72.8=B
B=34.4
2) 唔知E係邊所以答唔到不過角B就得
cosB=5/15
B=70.5
3)cos42=A/3
A=2.2
sin42=B/3
B=2
tan62=2/C
C=1.06
sin62=2/D
D=2.3
周界=2.3+1.06+1.5+2.2+3+1.5
=11.56
2008-03-12 09:31:06 補充：
希望你明白
參考: 自己
收錄日期: 2021-04-13 15:16:13
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080311000051KK03457