請給予詳盡步驟，答晒同多step 既比佢最佳回答！
P.62 (http://www.hkedcity.net/ihome/cabinet/get_file.phtml?CCI01092007_00001.bmp)
19) c) Using the results of part A and B, determine whether cos2Θ = 2cosΘ is always true.
20) (http://www.hkedcity.net/ihome/cabinet/get_file.phtml?CCI01092007_00001.bmp)
In the figure, the height of △ABC is H m. AB = 100m, ∠A = 40∘and ∠B = 30∘. Find the value of H, correct to 1 decimal place.
Maths 問題 (急)(10點)
2007-09-01 7:37 pm
回答 (1)
2007-09-09 9:32 am
✔ 最佳答案
我入唔到hkedcity,所以估下係唔係咁做19) cos2Θ=2cos^2Θ-1
so,cos2Θ is not equal to 2cosΘ
20)by sine formula,
AB/sinC=AC/sinB
100/sin110=AC/sin30
AC=53.209m (correct to 5 decimal place)
area of △ABC =1/2AB(AC)sinA
.....................=1710.1m^2 (correct to 5 decimal place)
(如果H係垂直於AB)
1/2AB(H)=1710.1
..........H=34.2m
(如果H係垂直於AC)
1/2AC(H)=1710.1
..........H=62.3m
(如果H係垂直於BC)
1/2BC(H)=1710.1
BC可用sine law揾
參考: 19)係Amath公式
收錄日期: 2021-04-13 13:14:09
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070901000051KK01567