ABC is a right - angled triangle with angle B = 90 degree, angle A = 70 degree. D is a point on BC such that AD = 0.8 m and DC = 1 m. Find angle DAB.
Note : This is a F.3 question, any method exceeding F. 3 level such as sine rule, cosine rule, quadratic equation etc. are not acceptable.
F. 3 Trig. Problem
2013-05-07 3:28 am
回答 (2)
2013-05-07 7:11 pm
✔ 最佳答案
Add a point on AC be E, which DE⊥AC∠DCE = 180 - 90 - 70 = 20 degree
DE = CD sin ∠DCE
DE = 1sin20
DE = 0.34202 (corr. to 5 d.p.)
sin ∠DAC = DE / AD
sin ∠DAC = 0.34202/0.8
∠DAC = 25.3106 (corr. to 4 d.p.)
∠DAB = 70 - 25.1306
∠DAB = 44.6894 (corr. to 4 d.p.)
PS 其實直接用(1/0.8) = (sin∠DAC / sin20) 會快好多...不就中三無D咁嘅野...
參考: 我, 計算機 (?)
2013-05-07 4:45 am
試吓用Pythagorean theorem
收錄日期: 2021-04-13 19:27:46
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