已知sin(7/12π+α)=2/3,求cos(α-11/12π)的值

lily8595 1年前 已收到1个回答 举报

tombbs035 幼苗

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∵sin(7/12π+α)=2/3,
α-11/12π=-3π/2+(7π/12+α)
∴cos(α-11/12π)
=cos[-3π/2+(7π/12+α)]
=cos[-3π/2+2π+(7π/12+α)]
=cos[π/2+(7π/12+α)]
=-sin(7π/12+α)
=-2/3

1年前

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