maths
2007-05-31 1:19 am
The figure shows triangleABC with AC=10cm,AB=8cm and 角BAC=60度.M and N are mis-point of AB and BC respectively.Find the area of the quadrilateral ACNM.
回答 (2)
2007-05-31 2:30 am
✔ 最佳答案
First, you should find out the line BC by COSLAW : square BC = square AB + square AC -2(AB)(AC)cosBAC
square BC = 64+100-2x8x10x0.5
BC=9.16515 cm
then find out the angle ABC by sinLaw :
10/sinABC=9.16515/sin60
angle ABC = 70.893395 degree
finally use area ABC - area BMN = area ACNM
area ACNM =0.5 x AB x AC x sinBAC - 0.5 x AB/2 x BC/2 x sin ABC
= 0.5 x 8 x 10 x sin60 - 0.5 x 4x 4.58258 x sin70.893395
= 26.0 cm square
2007-05-31 2:56 am
給你一個較簡單的方法，不需用到cosine law 和sine law：
圖片參考：http://i193.photobucket.com/albums/z215/lechocoona/maths/32.gif?t=1180522571
圖片參考：http://i193.photobucket.com/albums/z215/lechocoona/maths/32.gif?t=1180522571
收錄日期: 2021-04-20 23:32:34
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070530000051KK02393