f.3 math (bearings)

因為C係A東面
so角NAC=90
角BAC=90-18=72
我將B延長到AC相交於D
角BDC=BDA=90
so三角形BDA同DBC係直角三角形
AD長度=13cos72=4.01km
角DBC=180-128=52......(直線上的鄰角)
DC長度=21sin52=16.5km
DC+AD=AC
16.5+4.01=20.6km

2010-05-22 12:52:47 補充：
so角NAC=90
我指係A點個N
我轉番eng..sorry
我無轉eng個d係解你聽,唔係答題用

2010-05-22 12:52:50 補充：
Because the island C is due east of island A
So angle NAC=90
angle BAC=90-18=72
Extend B and meet AC on D
angle BDC=BDA=90
AD=13cos72=4.01km
angle DBC=180-128=52.........(angles on the st.line)
DC=21sin52=16.5km
DC+AD=AC
16.5+4.01=20.6km
So the distance between A and C is 20.6km

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