※ 引述《sincetoday (sincetoday)》之銘言:
: sin20sin40sin80 =? (單位為度)
: 今天碰到這題一時想不出來,
: 謝謝!
8*sin20sin40sin80
= 4(cos20-cos60)sin80
= 4cos20sin80 - 2sin80
= 2(sin100 + sin60) -2sin80
= 2sin60 = sqrt(3)
sin20sin40sin80 = sqrt(3)/8
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