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2條f.2升f.3數學(三角形)

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最佳解答:

您好,我是 lop****** ,高興能解答您的問題。 (1) ∠DAC = ∠ADC = 72° ∠ACD = 180° - 72° - 72° = 36° ∠BCD = 36°/2 = 18° ∠BDC = 180° - 72° = 118° x = 180° - 18° - 118° = 44° (2) ∠AEC = 180° - 78° = 112° ∠EAC = ∠ECA ∠EAC = (180°-112°)/2 = 78°/2 = 39° ∠CAD = ∠EAC = 39° ∠ACD = ∠ADC = x x = (180°-39°)/2 = 141°/2 = 70.5° ∠ECA = 39° ∠ACD = 70.5° y = 180° - 39° - 70.5° = 70.5°

其他解答:

1. ∠CAB=72° (BASE ∠ ISOS. △) ∠ACD+72°+72°=180° (∠ SUM OF △) ∠ACD=36° ∠BCD=36°/2 =18° x+72°+18°+36°=180° (∠ SUM OF △) x=54° 2. 設 a=∠EAC. a=∠ACE (BASE ∠ ISOS. △) a+a=78°(EXT. ∠ OF △) a=39° ∠EAC=∠DAC(GIVEN) ∠DAC=39° x=∠ACD (BASE ∠ ISOS. △) 2x+39°=180° (∠ SUM OF △) x=70.5° ∠B+70.5°+39°+39°=180° (∠ SUM OF △) ∠B=31.5° y+31.5°+78°=180° (∠ SUM OF △) y=70.5°
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