Re: [中學]
※ 引述《gunhello (資深動感超人)》之銘言:
: https://iiil.io/P8Yw
: 拜託各位高手,可以幫我解決這個幾何問題嗎?謝謝。
draw CD, we have angle BCD = 50deg and angle DCE = 30 deg
let BC = 1, CD = x, AC = y
1/sin50 = x/sin80
x = sin80/cos40 = 2sin40
1/sin30 = x/sin(DEC)
sin(DEC) = x*sin30 = 2sin40sin30 = sin40
angle DEC = 40deg
so angle DEF = 40-10 = 30 deg#
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