Math Ap. of trig. in 3D(20s)

22a)cosㄥCOA= (OC² + OA² - CA²) / (2 OC OA)= ( (h / tan30°)² + 60² - (h / tan60°)² ) / (2 (h / tan30°) (60) )= (3h² + 3600 - h²/3) / ( 2 (√3 h) (60) )= (8h² + 10800) / (360 √3 h)= (h² + 1350) / (45√3h)
b)cosㄥCOB= (OC² + OB² - CB²) / (2 OC OB)= ( (h / tan30°)² + 90² - h² ) / ( 2 (h / tan30°) (90) )= ( 3h² + 8100 - h² ) / (180√3 h)= (h² + 4050) / (90√3 h)
c)cosㄥCOA = cosㄥCOB(h² + 1350) / (45√3 h) = (h² + 4050) / (90√3 h)2(h² + 1350) = h² + 4050h = 15√6
d)cosㄥCOB = ((15√6)² + 4050) / (90√3 (15√6))= 5400 / (1350√18)ㄥCOB = 19.5°The compass bearing of B from C is N 19.5° E .

2011-10-16 14:28:38 補充：
The compass bearing of B from O is N 19.5° E .