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两个关于三角函数计算的高中数学题
1.sin20°·sin40°·sin60°·sin80
2.sin6°·cos24°·sin78°·cos48
这两题解法思路一样么?
人气:273 ℃ 时间:2020-05-26 21:18:41
解答
sin(6°)cos(12°)cos(24°)cos(48°)
=sin6°·cos6°·cos12°·cos24°·cos48°/cos6°
=sin12°·cos12°·cos24°·cos48°/2cos6°
=sin24°·cos24°·cos48°/4cos6°
=sin48°·cos48°/8cos6°
=sin96°/16cos6°
=sin(180°-96°)/16cos6°
=sin84°/16cos6°
=1/16
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