敏健從家門 A 依方位角 220 度的方向騎單車出發.他以 28 km/h 的速率前進經 45 分鐘到達 B 點 .然後,他改變方向以方位角 135 度及原有車速率至 C 點,而 C 點位於 A 的正南方.
求由 B 騎車至 C 所需的時間
Maths (10 marks)
2009-05-24 3:08 am
回答 (2)
2009-05-24 3:59 am
✔ 最佳答案
The answer is as follows:圖片參考：http://i320.photobucket.com/albums/nn347/old-master/090523_1.jpg?t=1243079916
2009-05-24 4:03 am
According to the description above, A, B and C should form a triangle where
AB=28*(45/60)= 21km
angle CAB=220degree -180 degree =40 degree
angle ABC= (90-40)(corresponding angle suppl) + (135-90)
=50+45=95
angle ACB=180-95-40 (angle sum of triangle) =45 degree
By sine law,
21/ sin 45 = BC / sin 40
BC=19.09km
Time it takes from B to C
=19.09/28
=0.68 hour
AB=28*(45/60)= 21km
angle CAB=220degree -180 degree =40 degree
angle ABC= (90-40)(corresponding angle suppl) + (135-90)
=50+45=95
angle ACB=180-95-40 (angle sum of triangle) =45 degree
By sine law,
21/ sin 45 = BC / sin 40
BC=19.09km
Time it takes from B to C
=19.09/28
=0.68 hour
參考: ME
收錄日期: 2021-04-29 18:22:17
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