圖片參考:http://imgcld.yimg.com/8/n/HA00656648/o/701107270103213873433680.jpg
更新1:
Yes, there are some mistakes 1) It should be sin(A+B)sin(B-A) instead of sin(A+B)sin(A-B) 2) It should be cos^2 A - cos^2 B - cos^2 C= -1 instead of cos^2 A - cos^2 B + cos^2 C= -1
更新2:
Question(iii), Why sin (π/2 + x - y) sin (π/2 - (x + y)) = cos -(x - y) cos(x + y) should it be cos(x - y) cos(x + y)