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幼苗
共回答了20个问题采纳率:90% 举报
由已知得:
sin(7/6π+α)
=sin(π + 1/6π+α)
=-sin(1/6π+α)
=-sin[π/2 - (π/3 -α)]
=-cos(π/3 -α)
=-cos(α -π/3)
=1/3
那么:cos(α -π/3)=-1/3
所以:
sin(2α-7/6π)
=sin(2α-2/3π - π/2)
=-sin[π/2 - (2α-2/3π)]
=-cos(2α-2/3π)
=-[2cos平方(α-π/3) -1]
=-(2*1/9 -1)
=7/9
1年前
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