Re: [中學] 三角函數計算
: 感謝～
以下都代表角度
(sin80)^2 + (cos50)^2 - cos80*sin50
= (sin80)^2 + (cos(80-30))^2 - cos80*sin(80-30)
= (sin80)^2 + (√3*cos80/2 + sin80/2 )^2 - cos80*(√3*sin80/2 - cos80/2)
= (sin80)^2 + 3(cos80)^2/4 + (sin80)^2/4 + √3*cos80*sin80/2
- √3*cos80*sin80/2 + (cos80)^2/2
= 5[(sin80)^2 + (cos80)^2]/4 = 5/4
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※ 編輯: FAlin (114.47.174.114 臺灣), 10/14/2019 23:10:10
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