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若sin(α+π/6)=1/3,则cos(2π/3-2α)的值为
人气:156 ℃ 时间:2020-01-27 02:56:13
解答
cos(2π/3-2α)
=-cos[π-(2π/3-2α)]
=-cos(π/3+2α)
=-cos[2(π/6+α)]
=-{1-2[sin(π/6+α)]^2}
=-(1-2/9)
=-7/9
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