Re: [中學] 三角函數一題
※ 引述《alamabarry (.............)》之銘言：
: ※ 引述《wa007123456 (大笨羊)》之銘言：
: : 題目:
: : sin(5度)*sin(25度)*sin(35度)*sin(55度)*sin(65度)*sin(85度) = ?
: : 答案: 1/64
: : 謝謝各位高手><
: 兩倍角公式跟餘角互換
: =sin5*cos5*sin25*cos25*sin35*cos35
: =[sin10*sin50*sin70]/8
: =cos20*cos40*cos80/8
: =sin20*cos20*cos40*cos80/8*sin20
: =sin40*cos40*cos80/16*sin20
: =sin80*cos80/32*sin20
: =sin160/64*sin20
: =1/64
此解法
亦出現在
陳一理所編著的"三角函數"
也可供參考...
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