Math(Application of Trigonometry)

2007-05-18 8:47 pm
1.In the figure,ABC is a traingle.D is a point on BC such that AD bisects angle A.If B=70°,C=40° and BC =12cm,
(a)find the length of AC.
(b)find the length of AD.

回答 (3)

2007-05-18 9:06 pm
✔ 最佳答案
(a)A=180°-70°-40°=70°,由於A=B,因此ABC是等腰三角形,因此AC=BC=12cm。
(b)不知道你學了sin law未,不過如果沒猜錯的話應該是用sin law吧!由於AD二等分了角A,因此角CAD=70°/2=35°,by part (a),AC=12cm,因此by sin law,AC/sin ADC=AD/sin C,由於ADC=180°-35°-40°=105°,因此AD=12 sin 40°/sin 105°=7.99cm
參考: 自己
2007-05-18 9:42 pm
(a)

12/ sin 70 = AC/ sin70

AC = 12cm

(b)

AD/ sin 70 = 6 / sin 35

AD = 9.83cm (to 2 d.p.)
2007-05-18 9:06 pm
A=180-70-40=70
SO AC=BC=12cm

traingleADC
angleDAC=70/2=35
SO AD/sin40=12/sin(180-40-35)


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