第7條
In parallelogram ABCD,AB=2,BC=4,the angle between the diagonals
AC and BD is 45'.
Find the area of ABCD
我想要solution +ans thx
圖係下面(保證無毒)
http://i289.photobucket.com/albums/ll221/sam7162005/IMG.jpg
一條好簡單既a maths (F.4 Level)
2009-03-31 4:48 am
回答 (1)
2009-03-31 6:10 am
✔ 最佳答案
Interesting question, let AE=x,BE=ySince in triangle ABE
4=x^2+y^2-2xycos45
in triangle BCE
16=x^2+y^2-2xycos135=x^2+y^2+2xycos45
=>4xycos45=12
or xy=6/SQRT(2)
Now, the key step is the area of ABCD=4*area ABE
So area of ABCD
=4*(1/2)xysin45
=6
收錄日期: 2021-04-26 13:06:23
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20090330000051KK01597