sin(a+b) = sin a cos b + cos a sin b = 1/2
sin(a-b) = sin a cos b - cos a sin b = 1/3
sin a cos b = ½ (1/2 + 1/3) = 5/12 <------------
cos a sin b = ½ (1/2 + 1/3) = 1/12 <----------
tan a / tan b = (5/12) / (1/12) = 5
So, tan a : tan b = 5 : 1.
箭咀果到點黎...不明白
amths@@
2007-02-22 9:42 am
回答 (1)
2007-02-22 9:50 am
✔ 最佳答案
sin(a+b) = sin a cos b + cos a sin b = 1/2...........(1)sin(a-b) = sin a cos b - cos a sin b = 1/3.............(2)
將(1)+(2) (sin a cos b + cos a sin b)+(sin a cos b - cos a sin b)=1/2+1/3
2sin a cos b=1/2+1/3
所以 sin a cos b=½(1/2+1/3)=5/12
將(1)-(2) (sin a cos b + cos a sin b)-(sin a cos b - cos a sin b)=1/2+1/3
2cos a sin b=1/2-1/3
所以 cos a sin b=½(1/2-1/3)=1/12
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收錄日期: 2021-05-02 20:25:53
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